3 (BC 401 ABAP Objects)

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BC401 Partner

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Education Website

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Participant Handbook Course Version: 2004 Q1 Course Duration: 5 Day(s) Material Number: 50065633

An SAP course - use it to learn, reference it for work

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SAP

mySAP Technology

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ABAP Objects

Copyright Copyright © 2004 SAP AG. All rights reserved. No part of this publication may be reproduced or transmitted in any form or for any purpose without the express permission of SAP AG. The information contained herein may be changed without prior notice. Some software products marketed by SAP AG and its distributors contain proprietary software components of other software vendors.

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About This Handbook This handbook is intended to complement the instructor-led presentation of this course, and serve as a source of reference. It is not suitable for self-study.

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American English is the standard used in this handbook. The following typographic conventions are also used.

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Example text

Emphasized words or phrases in body text, titles of graphics, and tables

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Names of elements in the system. These include report names, program names, transaction codes, table names, and individual key words of a programming language, when surrounded by body text, for example SELECT and INCLUDE.

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Also used for cross-references to other documentation both internal (in this documentation) and external (in other locations, such as SAPNet).

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© 2004 SAP AG. All rights reserved.

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BC401

Type Style

Description

Example text

Screen output. This includes file and directory names and their paths, messages, names of variables and parameters, and passages of the source text of a program.

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Exact user entry. These are words and characters that you enter in the system exactly as they appear in the documentation.

<Example text>

Variable user entry. Pointed brackets indicate that you replace these words and characters with appropriate entries.

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Icons in Body Text The following icons are used in this handbook. Meaning

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For more information, tips, or background

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Exception or caution Procedures

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Indicates that the item is displayed in the instructor’s presentation.


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Note or further explanation of previous point

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About This Handbook

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Contents Course Overview ............................................................................. vii

The Object-Oriented Programming Model .............................................. 93 Analysis and Design with UML........................................................... 106 Fundamental Object-Oriented Syntax Elements ...................................... 120

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Unit 2: Introduction to Object-Oriented Programming .............................. 91

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Course Goals................................................................................ viii Course Objectives .......................................................................... viii

Unit 1: Completing the Procedural Parts of ABAP Objects ..........................1 Unicode-Compatible String Processing in ABAP Objects for SAP Web Application Server 6.20 ................................................................................ 3 Optimized Working with Internal Tables ................................................. 22

SAP Use

Unit 4: Object-Oriented Repository Objects ..........................................305 Global Classes and Interfaces ........................................................... 307 Special Object-Oriented Programming Techniques ................................... 352 Persistent Objects in ABAP Objects for SAP Web Application Server 6.20 ...... 369

Unit 5: Exception Handling and Dynamic Programming ...........................381

Appendix 1: Calling Programs and Passing Data

.................................465

Index ............................................................................................483

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Exception Handling in ABAP Objects for the SAP Web Application Server 6.20 . 383 Dynamic Programming with ABAP Objects for the SAP Web Application Server 6.20 ........................................................................................... 422

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Inheritance and Casting................................................................... 185 Interfaces and Casting .................................................................... 226 Events ....................................................................................... 263

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Unit 3: Object-Oriented Concepts and Programming Techniques ...............183

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Course Overview Only

Furthermore, you will become familiar with the tools in the ABAP Workbench that are used for object-oriented programming with ABAP Objects.

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Many of the programming techniques, tools, and syntax elements in this course are already available as of SAP R/3 4.6A. The ones that are not are available as of SAP Web AS 6.10. There are only minimal differences between SAP Web AS 6.10 and SAP Web AS 6.20 and which relate to ABAP Objects and ABAP Workbench.

Target Audience This course is intended for the following audiences: • •

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Development project managers ABAP Objects developers


Partner

The SAP technology component SAP Web Application Server, or SAP Web AS for short, is embedded in the SAP NetWeaver solution and is therefore the technical basis for nearly all SAP solutions. That means that you can use the knowledge and skills you gain in this course for all solutions that were developed with ABAP Objects, not just for developing within SAP ERP.

SAP

SAP

The course’s third part will introduce you to programming techniques that partially use object-oriented elements of ABAP Objects, but can also be used in procedural contexts.

Use

Partner

The first part of the course will introduce you to the procedural parts of ABAP Objects, as far as they are not covered in the sections that have been left out. The focus is on the second part of the course, which provides a step-by-step, extensive introduction to object-oriented development in ABAP Objects. This also includes an introduction to modeling.

Internal

This course will give you a comprehensive and detailed introduction into the programming techniques and the associated syntax of the ABAP Objects language. The only information that is not covered belongs to separate subject areas – like dialog programming, database access, and so on – that are already completely contained in other courses.

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Course Overview

BC401

Course Prerequisites Required Knowledge • • •

Programming experience SAPTEC (SAP NetWeaver: Application Platform Fundamentals) BC400 (ABAP Workbench - Concepts & Tools)

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This course will prepare you to:

Partner

After completing this course, you will be able to:

Course Objectives •

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SAP Software Component Information The information in this course pertains to the following SAP Software Components and releases: •

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Name and use the syntax elements for Unicode-compatible character string processing Use internal tables to optimum effect Use fundamental elements of object-oriented modeling in UML Create ABAP Objects programs that contain all useful object-oriented programming techniques Use the relevant tools to create object-oriented Repository objects Define, raise, and handle class-based exceptions Name and use the syntax elements for dynamic programming

SAP

• •

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Understand the details of object-oriented syntax elements in ABAP Objects and use these effectively Create object-oriented models of business applications Use the tools in the ABAP Workbench to develop object-oriented applications

SAP

•

Internal

Course Goals

Unit 1 Only

Unit Overview

The first lesson deals exhaustively with a topic that was completely new in the SAP Web AS 6.10.

SAP Use

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Unit Objectives After completing this unit, you will be able to:

• • • •

Describe the checking procedure that determines whether an ABAP Objects program can be executed in an SAP Unicode system Consider the special requirements for string processing in an SAP Unicode system Define internal tables Perform operations on internal tables Identify table kinds and use them appropriately in different situations

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Internal

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Unit Contents Lesson: Unicode-Compatible String Processing in ABAP Objects for SAP Web Application Server 6.20 ........................................................ 3 Exercise 1: Unicode-Compatible Character String Processing ........... 13 Lesson: Optimized Working with Internal Tables ................................ 22 Exercise 2: Internal Tables with an Unstructured Row Type............... 57

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The second lesson also contains a complete topic, but some of the contents will already be familiar to you. How much of the material you recognize will depend on the courses you have attended and the extent of your programming experience with ABAP Objects.

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In this unit, we will first deal with the purely procedural elements of the ABAP Objects programming language. That is, you can use the syntax elements introduced here either in or outside of an object-oriented context.

Internal

Completing the Procedural Parts of ABAP Objects

1

Unit 1: Completing the Procedural Parts of ABAP Objects

BC401

Exercise 3: Table Kinds......................................................... 63 Exercise 4: Data Processing and Transfer to Modularization Units (Optional) ......................................................................... 71

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Lesson: Unicode-Compatible String Processing in ABAP Objects for SAP Web Application Server 6.20

Lesson: Unicode-Compatible String Processing in ABAP Objects for SAP Web Application Server 6.20 Lesson Overview

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Lesson Objectives • •

Describe the checking procedure that determines whether an ABAP Objects program can be executed in an SAP Unicode system Consider the special requirements for string processing in an SAP Unicode system

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After completing this lesson, you will be able to:

SAP

SAP

Business Example You need to develop a Unicode-enabled ABAP Objects program in the SAP Web AS 6.20.

Use Internal

If other characters are to be processed, then you will need to load a different character set table. In this way, parallel, text-based processing in one system by users from different cultures is not possible without extra work being involved. Exchanging text-based data between systems in which different character set tables are valid will also cause problems. For this reason, the Unicode character set table has been defined. It is large enough to represent all the characters in the world. With a bit sequence length of 16, we now have 65,536 different codes. The Unicode character set according to ISO/IEC 10646 is supported since SAP Web AS 6.10.


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For internal representation of characters, software systems use bit sequences with fixed length. This length specifies the number of characters to be displayed altogether. The assignment between characters and bit sequence is done using the character set table. For example, the ASCII character set (length of 8 bits) consists of 256 characters.

Partner

System-Internal Representation of Characters Under Unicode

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Internal

In this unit, we will first introduce the terms used. After that, we will describe how you can find out whether or not you need to take any actions because of the Unicode-enablement of the SAP Web AS 6.20 and, if so, which actions these are.


BC401

SAP

In ABAP Objects, however, it is also possible to perform byte sequence processing. In many cases, the statements for this are the same as for string processing; however, they have different additions. Here, therefore, you need the correct decision in order to get semantically correct results. This will be discussed in more detail later in this unit.

Partner

Use

SAP

To execute the relevant syntax checks, you must set the indicator Unicode Checks Active in the program attributes. This is the standard setting in Unicode systems. In a Unicode system, you can only execute programs that have the Unicode indicator set.


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Internal

As of SAP Web AS 6.10, you can develop Unicode-compatible applications using ABAP Objects. The runtime system ensures Unicode-compatible internal representation of its character sets. Therefore, as long as you perform “safe” string processing – that is, you do not allow information on the internal length of a character to flow into your programs – you do not need to take care of anything further.

Often, however, you want to or have to reuse old source texts in which the above limitations have not been heeded. In such cases, you may have to make certain adjustments. Here, you will be supported, for the most part, by the ABAP Workbench. The syntax check has been extended to include an optional check for Unicode compatibility.

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Figure 1: Unicode Character Set Table

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If the Unicode indicator is set for a program, the syntax check and program are executed in accordance with the rules described in the SAP Library section about Unicode. (This is irrespective of whether it is in a Unicode or a non-Unicode system).

Only SAP Use Internal

Up to now, all arguments were interpreted implicitly in string processing as a field of the type C. As of SAP Web AS 6.10, there is a distinction between character-type and byte-type arguments. With the exception of statements that are obsolete anyway, character string commands in their standard form always expect character-type arguments for compatibility reasons. The statements are then converted by the system, character by character. For documentation reasons, you can use the optional addition IN CHARACTER MODE for these variants.

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Terms used: The following predefined data types are interpreted in Unicode programs as character-type: C, N, D, T, STRING, as well as structure types that contain - either directly or in substructures - solely components of these types (see also generic predefined data type CLIKE). In non-Unicode systems, a character of this type is one byte, and in Unicode systems, it is as long as a character on the relevant platform. Variables of the types X and XSTRING are described as byte-type.

Partner

Character and Byte Processing

SAP

If you wish to exchange data between Unicode and non-Unicode systems from SAP Web AS 6.10 onwards, you can use the statements EXPORT ... TO DATA BUFFER and IMPORT ... FROM DATA BUFFER, respectively. Your data is exported in XSTRING variables, but the internal Unicode-relevant additional information is also transferred. You can now exchange this byte sequence with other systems. The data is again extracted from the byte sequence with the additional information and represented internally, platform-based.

Use

The standard class CL_ABAP_CHAR_UTILITIES contains numerous characters, also CHARSIZE, that - at runtime - contain the length of a character, measured in bytes.

Internal

In programming terms, there are at least two ways to find out the internal length of a character in a certain platform: The predefined function CHARLEN() returns the length of the first character of the argument, measured in bytes.

Partner

If the Unicode indicator is not set, the program can only be executed in a non-Unicode system. For such programs, Unicode-specific changes of syntax and semantics do not apply. However, you can use all language enhancements introduced in connection with the conversion to Unicode.


BC401

Figure 2: Character String and Byte Sequence Processing

SAP Use Internal

The XSTRLEN function returns the length of byte sequence. It always expects byte-type variables and returns for type XSTRING the current length and for type X the defined length in bytes; null bytes at the end of fields are counted. Remember: The operators CO, CN, CA, NA, CS, NS, CP, and NP compare the contents of character-type data objects.

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The STRLEN function always expects character-type variables and returns their length in characters. With variables of type C, only the occupied length is relevant - that is, unlike with variables of the STRING type, trailing blanks are not counted.

Partner

Functions and Compare Operators

SAP

Exceptions to this simple rule exist only for the statements that are already obsolete anyway. The standard variant DESCRIBE FIELD ... LENGTH ... returns, for example, the internal length of a character string, that is, the number of bytes; with variables of type STRING, it even returns the length of the reference after it - hence always eight! Only if you have the optional addition IN BYTE MODE will the length in bytes be returned for STRING variables as well. And only if you have the optional addition IN CHARACTER MODE will the number of characters be returned. This kind of non-Unicode-compatible statement would be recognized as an error if the Unicode check was active. However, it should, if at all possible, be avoided. In such cases, use the predefined functions STRLEN and XSTRLEN instead.

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In short, only if you want to have explicit byte processing must you use the addition IN BYTE MODE. Do not use it if you want to process character strings.

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The corresponding variants of these statements for byte sequence processing are recognizable by the addition IN BYTE MODE. With this addition, the statements expect solely byte-type arguments and are also converted byte by byte.

BC401


For the contents of byte-type data objects, six further operators have been defined for SAP Web AS 6.10; they are distinguished from the originals by the prefix BYTE.

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Internal SAP

SAP

Figure 3: Lengths and Compares

To check whether the conversion is allowed at all, the system first creates the Unicode fragment view of the structures by grouping together adjacent components and alignment gaps. There are separate groups for character, byte, and numeric types (I,P,F). Adjacent character-type components of a structure are therefore only grouped together if there are no alignment gaps between these components. Adjacent byte-type components are grouped in the same way.

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Internal

For some data types there are, for technical reasons, specific alignment requirements that depend on the individual platforms. (In the memory, fields of this type must begin and end at specific addresses - for example, a memory address divisible by four, without remainder.) Within a structure, the runtime system, if necessary, inserts bytes before or after these components with alignment requirements to achieve the alignment needed. These bytes are referred to as alignment.

Partner

Use

Conversion Rules for Structures

If the fragments of the source and initial structures now match the type and length in the length of the shorter structure, conversion is allowed; if not, an error in the Unicode check will result. If the target structure is longer than the

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source structure, the character-type components of the remainder are filled with space characters. All other components in the remainder are filled with the type-specific initial values; alignment gaps are filled with null bytes.

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Internal

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Internal

If the structure is the target, the character-type parts of the remainder are filled with space characters and all other components with type-specific initial values. The conversion is not allowed if the structure is not purely character-type and the elementary data object is not type C.

Partner

The following rules apply for conversion of a structure into an elementary data object and vice versa: If the elementary data object is of type C, but the structure is not completely character-type, then conversion is only allowed when the structure starts with a character-type group and this group is at least as long as the elementary data object. The conversion then takes place between the first character-type group of the structure and the elementary data object.

SAP

SAP

Figure 4: Conversion Between Flat Structures

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Figure 5: Conversion Between Structures and Elementary Data Objects

Use

Hint: Internal tables can be converted if row types can be converted.

SAP Use

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Access with Offset and Length Specification Remember: Accesses to character and byte-type elementary data objects are allowed using offset and length specifications. For character-type variables, offset and length are interpreted character by character. If you have types X and XSTRING, the values for offset and length are interpreted byte by byte.

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You should try to avoid copying structure contents in this manner as much as possible. Instead, copy component by component. This way, no actions at all are required.

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SAP

SAP

Offset and length accesses to structures are only permitted in Unicode programs if the structure is flat and the offset and length specifications only contain character-type fields starting from the beginning of the structure. This means that the access will cause an error if the offset and length area contains both character-type and non-character-type components. If an offset/length access to a structure is allowed in a Unicode program, both offset and length specifications are always interpreted as characters.

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Figure 6: Access Using Offset and Length Specification for Elementary Data Objects

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Figure 7: Access Using Offset and Length Specification for Structures

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Where possible, you should try to avoid accessing contents of structures in this manner. Bear in mind that processing component by component and using character string operations is generally safer and more readable.

General Recommendations:

•

We recommend therefore that, as of now, you generally program “in a Unicode-compatible manner”; the indicator for Unicode Checks Active must always be set. In this manner, you avoid on the one hand generally unsafe techniques and obsolete statements; on the other hand, if you change your system to Unicode later on, no further checks or adjustments will be required.

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•

Always use the most current variants for (obsolete) statements. You will be supported to a large extent by the SAP Library. Program “safely” - that is, access structures component by component, provided there are no reasons to do otherwise. Also avoid offset/length access to entire structures.

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It should now be clear that you can avoid all the problems listed here very easily if you adhere strictly to the following during string processing or when working with structures:

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Exercise 1: Unicode-Compatible Character String Processing Exercise Objectives

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Business Example Assume that a data record of a specific flight is stored as an unstructured character string in the memory.

SAP Use Internal

For now, we will focus on a formatted list output.

Task 1: 1.

Only

Copy the template. Copy template: SAPBC401_DTOT_SPLIT_STRING Program name: ZBC401_##_SPLIT_STRING (Where ## is your two-digit group number). 2.

Activate your copy (or copies).

Continued on next page

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Using Unicode-compatible character string processing, the fragments of this character string are to be copied into structured data objects so that they can be processed further on the basis of the transparent table SFLIGHT.

SAP

Note: In practice, there are a few ways that this situation could arise. Typically, it may occur after data has been transferred from a different system or when data has been transferred remotely. Here, these cases are simulated by calling a function module that creates such data records based on the flight data model.

Use

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Internal

After completing this exercise, you will be able to: • Define structure types locally in the program • Define elementary and complex data elements • Split strings • Use conversion rules • Display the contents of data objects in lists

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Task 2: Familiarize yourself with the program and its existing functions. Pay special attention to the content of the data object DATASTRING after the function module call. Use the ABAP Debugger to do this, and/or display the character string in a list.

Only

Task 3:

1.

Remove the two leading separators from the character string first. Hint: Use the SHIFT statement.

SAP

Hint: Use the statements FIND and SPLIT. Split the contents of auxiliary variable SET_STRING at the separators into structure WA_FLIGHT_C. The structure is defined as local program structure type ST_FLIGHT_C. You still have to comment out the components of this structure type and assign them an appropriate type.

Task 4: Display the structured flight data as a list. 1.

As a test, display the fields of the structure WA_FLIGHT_C in a list.

2.

In the resulting list, you should have observed that some of the fields were displayed without formatting – for example, the PRICE field. Now improve this: Continued on next page

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2.

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For this, SET_STRING has to be defined appropriately.

SAP

Then copy the initial part up to the two closing separators to the auxiliary variable SET_STRING. Assume that there can be more characters after the two closing separators; these should remain in DATASTRING.

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Partner

Split a character string into its individual elements and copy it into structured data objects.

Internal

Hint: Think of the function module itself as a “black box”. A deeper understanding of how it works is not part of this exercise.

BC401


Convert the data you have extracted by copying it to data objects with suitable types. Also, not all components of WA_FLIGHT_C are to be processed further. Use the predefined structure WA_FLIGHT. The structure is defined as local program structure type ST_FLIGHT. You still have to comment out the components of this structure type and assign them an appropriate type.

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Display the contents of the structure WA_FLIGHT in a list.

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Hint: Use the appropriate formatting options for the WRITE statement for the FLDATE and PRICE fields.

SAP

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Solution 1: Unicode-Compatible Character String Processing Task 1: Copy the template. 1.

Copy template: SAPBC401_DTOT_SPLIT_STRING

Only

(Where ## is your two-digit group number). Carry out this step in the usual manner. Additional information is available in the SAP Library. Model solution: SAPBC401_DTOS_SPLIT_STRING 2.

Activate your copy (or copies). a)

Carry out this step in the usual manner. Additional information is available in the SAP Library.

SAP Use

Task 3: Split a character string into its individual elements and copy it into structured data objects. 1.

Remove the two leading separators from the character string first. Hint: Use the SHIFT statement.


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Internal

Hint: Think of the function module itself as a “black box”. A deeper understanding of how it works is not part of this exercise.

Partner

Familiarize yourself with the program and its existing functions. Pay special attention to the content of the data object DATASTRING after the function module call. Use the ABAP Debugger to do this, and/or display the character string in a list.

SAP

Task 2:

Use

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a)

Internal

Program name: ZBC401_##_SPLIT_STRING

BC401


Then copy the initial part up to the two closing separators to the auxiliary variable SET_STRING. Assume that there can be more characters after the two closing separators; these should remain in DATASTRING. For this, SET_STRING has to be defined appropriately. Hint: Use the statements FIND and SPLIT.

Only

2.

See the source code extract from the model solution

Split the contents of auxiliary variable SET_STRING at the separators into structure WA_FLIGHT_C.

a)


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The structure is defined as local program structure type ST_FLIGHT_C. You still have to comment out the components of this structure type and assign them an appropriate type.

Internal

a)

Task 4: Display the structured flight data as a list.

SAP

As a test, display the fields of the structure WA_FLIGHT_C in a list. a)


In the resulting list, you should have observed that some of the fields were displayed without formatting – for example, the PRICE field. Now improve this:

Internal

Display the contents of the structure WA_FLIGHT in a list. Hint: Use the appropriate formatting options for the WRITE statement for the FLDATE and PRICE fields. a)

See the source code extract from the model solution Continued on next page

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Convert the data you have extracted by copying it to data objects with suitable types. Also, not all components of WA_FLIGHT_C are to be processed further. Use the predefined structure WA_FLIGHT. The structure is defined as local program structure type ST_FLIGHT. You still have to comment out the components of this structure type and assign them an appropriate type.

Partner

Use

2.

SAP

1.


BC401

Result Source code extract:

SAPBC401_DTOS_SPLIT_STRING sapbc401_dtos_split_string.

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Only

REPORT

TYPES: mandt(3)

TYPE c,

carrid(3)

TYPE c,

connid(4)

TYPE n,

fldate(8)

TYPE n,

price(20)

TYPE c,

currency(5)

TYPE c,

planetype(10)

TYPE c,

seatsmax(10)

TYPE n,

seatsocc(10)

TYPE n,

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BEGIN OF st_flight_c,

SAP

SAP

paymentsum(22) TYPE c, seatsmax_b(10) TYPE n, seatsocc_b(10) TYPE n, seatsmax_f(10) TYPE n,

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seatsocc_f(10) TYPE n, END OF st_flight_c,

BEGIN OF st_flight, TYPE c,

connid(4)

TYPE n,

fldate

TYPE d,

price(9)

TYPE p DECIMALS 2,

currency(5)

TYPE c,

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Internal

carrid(3)

planetype(10) TYPE c, seatsmax

TYPE i,

seatsocc

TYPE i,

END OF st_flight. DATA: datastring

TYPE string,

set_string

TYPE string,


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wa_flight_c TYPE st_flight_c, wa_flight

TYPE st_flight.

START-OF-SELECTION.

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CALL FUNCTION ’BC401_GET_SEP_STRING’ * EXPORTING *

IM_NUMBER

= ’1’

*

IM_TABLE_NAME

= ’SFLIGHT’

*

IM_SEPARATOR

= ’#’

IM_UNIQUE

= ’X’

Partner

*

IMPORTING ex_string

= datastring

no_data

= 1

OTHERS

= 2.

Use

EXCEPTIONS

SAP

SAP

IF sy-subrc 0. MESSAGE a038(bc401). ENDIF.

Partner

Use

SHIFT datastring BY 2 PLACES. FIND ’##’ IN datastring. IF sy-subrc 0. MESSAGE a702(bc401).

Internal

ENDIF. SPLIT datastring AT ’##’ INTO set_string datastring.

Only

SPLIT set_string AT ’#’ INTO wa_flight_c-mandt wa_flight_c-carrid wa_flight_c-connid wa_flight_c-fldate wa_flight_c-price wa_flight_c-currency wa_flight_c-planetype wa_flight_c-seatsmax


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wa_flight_c-seatsocc wa_flight_c-paymentsum wa_flight_c-seatsmax_b wa_flight_c-seatsocc_b wa_flight_c-seatsmax_f wa_flight_c-seatsocc_f.

Internal

Only

MOVE-CORRESPONDING wa_flight_c TO wa_flight.

WRITE: / wa_flight-carrid, wa_flight-connid,

Partner

wa_flight-fldate DD/MM/YYYY, wa_flight-price CURRENCY wa_flight-currency, wa_flight-currency,

Use

wa_flight-planetype, wa_flight-seatsmax, wa_flight-seatsocc.

SAP

SAP Only

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Lesson Summary You should now be able to: • Describe the checking procedure that determines whether an ABAP Objects program can be executed in an SAP Unicode system • Consider the special requirements for string processing in an SAP Unicode system

Only

Internal

Related Information

Use

Partner

... about this subject is available in the SAP Library and the ABAP keyword documentation for the individual statements.

SAP

SAP Only

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BC401

Lesson: Optimized Working with Internal Tables Lesson Overview

Only

Therefore, this lesson goes far beyond the material that you may have covered in other courses about internal tables.


Internal Tables as Dynamic Data Objects

Use internal tables for data processing in your program. Choose the most suitable table kinds and the method of processing that is best for the runtime.

Internal

Internal tables are dynamic data objects that can hold any number of rows of a fixed type. The number of rows in an internal table is limited only by the capacity of the specific system with which you are working. You can define the row type of an internal table to include elementary, structured, or even table-type, and can be as complex as you want to make it.

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Internal tables are data objects that allow you to store datasets with a fixed structure in memory. The data is stored row by row in memory. Each row has the same structure. You can also refer to each component in a row as a column in the internal table. You refer to each row in the internal table as a table row or table entry.

Partner

Business Example

SAP

SAP

Define internal tables Perform operations on internal tables Identify table kinds and use them appropriately in different situations

Use

• • •

Use

Partner

Lesson Objectives

Internal

This lesson covers nearly all aspects of working with internal tables. It contains all necessary information, starting with the definition of this special data type through to recommendations for using different table kinds and methods of access – specifically in light of runtime requirements. Also, virtually all syntactic possibilities are listed here for the first time.

Lesson: Optimized Working with Internal Tables

Internal

Only

BC401

Figure 8: Attributes of Internal Tables

Row type The row type defines the attributes of the individual columns. You normally enter a structure type, but any data type is possible.

SAP Use

•

Key access – like database tables – works via field contents.

•

For index access, unlike for database tables, the system assigns row numbers to certain kinds of internal tables. This means that you can sometimes use the index to access rows in the table. Example: Read-access to the data record with index 5 returns the fifth data record from the internal table.

The table kind is another characteristic of internal tables. Internal tables can be divided into three table kinds, depending on the possible access types.

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Internal

Example: Using the search term UA 0007 for read access to an internal table with the unique key CARRID CONNID and data as specified above will result in exactly one data record.

Partner

Access type

SAP

Key definition The key columns and their sequence determine the criteria by which the system identifies table rows. You can define the key as either UNIQUE or NON-UNIQUE. The uniqueness of the key must be compatible with the access type you have chosen for the table. If the key is unique, there can be no duplicate entries in the table.

Use

Partner

The data type of an internal table is fully specified by its:


BC401

Standard tables The row number is maintained internally. Both index and key access are possible. Sorted tables Data records are sorted by the key and stored in these tables. Their index is also maintained internally. Both index and key access are possible.

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Partner

Internal

Hashed tables The runtime-optimized data records are maintained here. This requires a unique key. Hashed tables only allow for key access.

• • •

Standard tables are usually used with index access. Sorted tables are ideally used with unique keys and fixed sorting. For hashed tables, runtime optimization generally occurs only with read access and a unique key.

Defining Internal Tables For internal tables, as for other forms of data objects, there are three fundamentally different possible combinations for specifying the data object’s type:

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Internal

On a case-by-case basis, the table kind is decided by which access types will primarily be used with the table entries.

Partner

Use

SAP

SAP

Figure 9: Link Between Table Kind and Access Type

BC401


Possibilities for Specifying the Type of an Internal Table • • •

with an implicit (bound) type with a local, explicitly defined type with a global, explicitly defined type

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Internal

We fill focus on the first two possibilities, since we think that the creation of a table kind in the ABAP Dictionary is very easy once the concepts in this section are familiar.

This must be followed by a row type to determine the nesting depth of the internal table. It can be defined locally or globally or it can be a data object. You specify the table key using WITH key_def. key_def includes the names of all the key fields in order and specifies whether the key is to be UNIQUE or NON-UNIQUE

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Internal

There are three syntax additions that you use to specify a table kind for your internal table: STANDARD TABLE, SORTED TABLE and HASHED TABLE.

Partner

Use

SAP

SAP

Figure 10: Definition of Tables or Table Kinds In a Local Program


BC401

. •

The combination of the table kind and the key definition is not arbitrary, because of the special support that certain table kinds receive with specific types of read access. You can use any of the following combinations:

Partner

For standard tables Only non-unique

Use

For sorted tables Unique or non-unique

There is a standard type for internal tables. You can use a shorter syntax to define it.

Use

Interpretation of the Short Syntax by the Runtime System DATA itab_name TYPE [STANDARD] TABLE OF line_type [WITH NON-UNIQUE DEFAULT KEY].


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Internal

DATA itab_name TYPE TABLE OF line_type.

Partner

Shorter Syntax for the Definition of Standard Tables with a Bound Type

SAP

SAP

For hashed tables Only unique

26

Internal

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•

Either create a user-defined key by naming the key fields after KEY, or specify the standard key using the WITH DEFAULT KEY addition. The standard key consists of all the fields with character-type data types (C, N, D, T, X, STRING, XSTRING). Alternatively, use the pseudo-component table_line, if you are specifying a table without a structured row type, or if the entire row is being used as the key.

BC401


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Internal

SAP

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Internal

Partner

The DEFAULT KEY short form means that all non-numeric fields are used to create the key. They are used in the sequence in which they occur in the row type. In this case, the keys CARRID, CONNID, and DISTID are defined. The key is non-unique.

SAP

The above example shows the definition of an internal table (TT_DISTANCE) using a local table kind (TT_DISTANCE_TY), which itself uses a local row type (S_DISTANCE_TY). Therefore, the defined internal standard table has the columns CARRID, CONNID, DISTANCE, and DISTID.

Use

Figure 11: Standard Table With a Local, Explicitly Defined Type – Example

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28

Allocation step

No addition

With the addition INITIAL SIZE n

0

8 bytes

8 bytes

1

8 - 16 KB

Row width * n bytes

2

8 - 16 KB

2 * row width * n bytes

every additional step

8 - 16 KB

8 - 16 KB


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Internal

Memory Allocation and Initial Size

Partner

For table kinds defined in a program, you can use the optional INITIAL SIZE addition to specify the number of rows that the runtime system should reserve when it instantiates the data object.

SAP

The above example shows the definition of a sorted table and a hashed table. Both tables have the same row type as the standard table on the previous slide. Note that the contents of the tables are in a different order. For sorted tables, the sequence of the entries in the internal table is determined by the sequence of the fields in the key definition.

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Internal

Figure 12: Sorted and Hashed Table – Examples

BC401


Specifying the number of rows is useful when your internal table is part of another internal table’s row type (nested internal tables). However, if your table needs more rows at runtime, it will not be limited in size by this addition, since the runtime system frees the necessary memory dynamically. (Internal tables are dynamic data objects.)

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Internal

SAP

Internal Table Operations

To keep the syntax patterns clear, we will start by assuming that we are dealing with an internal table with no header line and that data is exchanged using a row-compatible query area. Access using field symbols will be examined separately later.

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Internal

This section contains a detailed summary of the syntactical possibilities for managing data records using internal tables. Whether you are using key access or index access is specified individually for each statement.

Partner

Use

Incomplete table kinds are known as generic. You can only use them to assign types to table-type interface parameters.

SAP

Figure 13: Generic Table Kinds

standard table The data record is appended to the internal table, just as with the APPEND statement.

You can use these statements for inserting with all three types of tables. The technical implementation of the statements varies slightly according to the table kind.

SAP Use

With a unique key, and if the data record is already present, the record is not inserted and the return value SY-SUBRC is set to 4.

You can only use the COLLECT statement with internal tables whose non-key fields are all numeric (type I, P, or F). The COLLECT statement adds the work area to an internal entry with the same type or, if there is none, adds a new entry to the table. It searches for the entry according to the table kind and defined key. If it finds an entry in the table, it adds all numeric fields that are not part of the key to the existing values. If it does not, the content of the query area is inserted as a new entry.

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Internal

When index tables are inserted successfully, the system field SY-TABIX is set to the insert position.

Partner

hashed table The data record is appended, but an entry is made in the hash index.

SAP

Sorted table With a unique key, the table is sorted ascendingly in accordance with the key definition. With a non-unique key, the data record is included before any duplicate data records that may be present.

Use

Figure 14: Inserting With Key Access

Internal

Only

BC401

Partner


BC401


Use

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Only

Internal

Figure 15: Appending and Inserting with Index Access

SAP Use

Caution: When you use these statements, you must ensure that the sort sequence remains untouched. Therefore, we recommend using index access only with standard tables. This statement is an easy way to make a ranked list: APPEND wa INTO rank_itab SORTED BY f.

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Internal

Hint: If you want to insert a set of rows from an index table into another index table, you should use the INSERT LINES OF variant instead.

Partner

Within a loop, the INSERT statement adds the data record before the current record in the table.

SAP

When you are inserting and you specify an index that is more than one greater than the current number of rows, nothing is inserted and the SY-SUBRC return value is set to 4.


BC401

The data record in the query area wa is sorted descendingly by the maximum length as specified by INITIAL SIZE and inserted into the ranked list rank_itab. However, this only happens if the data record fits into the list according to sort criterion f. Caution: This means that a different data record may be removed from the ranked list. In this case – unlike all other cases – the INITIAL SIZE addition sets the length of the internal table.

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Internal

If no row could be found for the key or the logical condition, nothing is changed or deleted and the return value SY-SUBRC is set to 4. In the TRANSPORTING addition, you can restrict the data transport to selected components. You can program almost any logical expression after WHERE. The only restriction is that the first field in each comparison must be a component of the row structure (see the corresponding Open SQL statements). You can pass component names dynamically. This statement is an easy way to delete duplicates:

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Internal

If you use these key accesses with the variants FROM wa, the key fields in the work area must be filled.

Partner

Use

SAP

SAP

Figure 16: Changing and Deleting With Key Access

BC401


DELETE ADJACENT DUPLICATES FROM itab [ COMPARING {f_1 .. f_n} | ALL FIELDS } ] .

Only

The best way to delete the entire internal table is to use any of the following three statements:

Partner SAP Use

Only

Internal

Partner

CLEAR For internal tables without a header line, it has the same effect as REFRESH. Unlike for other data objects, no initial values are inserted into the internal table.

SAP

FREE Removes all data records and releases the memory they were using. If new data records are inserted later, the system allocates new memory to them.

Use

REFRESH Removes all data records but reserves the memory they were using for future insertions, presuming the memory is not required elsewhere in the system.

Internal

If there are rows with identical key field contents that are directly below each other, all but the first row is removed. The exclusive comparison of the key fields can be removed using the COMPARING addition. If you used SORT to sort by the desired fields, there are definitely only unique data records left, as you instructed.

Figure 17: Changing and Deleting with Index Access

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The statements listed here can be used freely with both standard and sorted tables. When you are changing or deleting and you specify an index that is greater than the current number of rows, nothing is changed or deleted and the SY-SUBRC return value is set to 4. When you change a single row, you can specify the fields that you want to change using the TRANSPORTING addition.

Only

Use

Partner

Hint: If you want to delete a set of rows from an internal table, use the variants DELETE itab FROM .. TO .. or WHERE .. instead of a loop.

Internal

Within a loop, MODIFY changes the current data record.

SAP

SAP

Use

The STABLE addition means that the relative order of records with the same sort key is not changed. The AS TEXT addition selects the culture-specific sort sequence. For example, the sort is not case sensitive.

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Internal

In the standard form, the SORT statement sorts ascendingly. Thus, the ASCENDING addition is optional. For a descending sort, use the DESCENDING addition. Along with the AS TEXT addition, these can be used independently for each sort criterion (c1 to cn).

Partner

Figure 18: Sorting Standard and Hashed Tables


Figure 19: Reading with Key Access

If you use the WITH TABLE KEY addition in the second variant, you must also specify the key fully. Otherwise, the system searches according to the sequence of fields that you have specified, using a binary search where possible.

SAP Use

After a successful search, the total number of rows in the table is written into the system field SY-TFILL and the rows length is written into the system field SY-TLENG. When index tables are searched successfully, the system field SY-TABIX is set to the found position. You can use the COMPARING addition to check that specified field contents of the found data records and the query area are identical. Caution: When the search is successful but the field contents are different, the return value SY-SUBRC is set to 2.

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Internal

If there are duplicate records that match your search criteria, the first data record that is found is displayed.

Partner

Caution: In this case, you must sort the table by the relevant fields first. Otherwise, the data record might not be found, even though it is contained in the table.

SAP

Hint: You can force the system to use a binary search with a standard table using the BINARY SEARCH addition.

Use

Partner

To read individual data records using the first variant, all fields of query area WA_1 that are also key fields of the internal table ITAB must be filled. WA_1 and WA_2 may be identical.

Internal

Only

BC401


BC401

In the TRANSPORTING addition, you can restrict the data transport to selected fields.

Use

Partner

Alternatively, you can use field symbols or references to access data. To do so, use ASSIGNING or REFERENCE INTO ref_line. This will be discussed in more detail later.

Internal

Only

Instead of the target clause INTO wa [ COMPARING ] [ TRANSPORTING ] , you can also use TRANSPORTING NO FIELDS . Then no more data is transported. This variant can also be used for existence checks.

SAP Use

Only

Internal

When you are changing or deleting and you specify an index that is more than the maximum number of rows, nothing is read and the SY-SUBRC return value is set to 4.

Partner

The statement listed here can be used freely with both standard and sorted tables. The specified additions and the return value function as described above.

SAP

Figure 20: Reading a Single Record with Index Access

Figure 21: Loop Processing with Key Access

In the LOOPAT ... ENDLOOP structure, the statements within the loop are applied to each data record in turn. The INTO addition copies entries one at a time into the work area.

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The system places the index of the current loop pass in the system field SY-TABIX. When the loop has finished, SY-TABIX has the same value that it had before the loop started. Inserting and deleting rows within a loop affects the subsequent loop passes.

Only SAP

SAP

Hint: You can use AT NEW ... ENDAT to achieve control level processing in loops with internal tables. For more information, see the SAP Library and/or the ABAP keyword documentation about AT.

Use

Alternatively, you can use field symbols or references to access data. To do so, use ASSIGNING or REFERENCE INTO ref_line. This will be discussed in more detail later.

Internal

Instead of the target clause INTO wa, you can also use TRANSPORTING NO FIELDS . Then no more data is transported. This variant can also be used for existence checks or counting.

Partner

Use WHERE to specify virtually any logical condition for the search results. If no data records match these conditions, nothing is read and the SY-SUBRC return value is set to 4.

The statement listed here can be used freely with both standard and sorted tables. Using FROM to specify the starting index, TO to specify the stopping index, and WHERE, you can set very flexible limits for the search results. If you specify an index after FROM that is more than the maximum number of rows, nothing is read and the SY-SUBRC return value is set to 4. Once again, the additions and return value function as described above.

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Figure 22: Loop Processing with Index Access


BC401

Use

Partner

Only

Internal

Figure 23: Internal Tables With or Without Header Line – Comparison

SAP Use Internal

Within object-oriented contexts, you can only use internal tables without a header line. You can always address the body of an internal table itab explicitly by using the following syntax: itab[] This syntax is always valid, whether the internal table has a header line or not.

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However, internal tables with a header line do offer shorter syntax in several statements (APPEND, INSERT, MODIFY, COLLECT, DELETE, READ, LOOP AT).

Partner

The way in which the system interprets the name depends on the context. For example, the MOVE statement applies to the header line, but the SEARCH statement applies to the body of the table. To avoid confusion, you are recommended to use internal tables without header lines. This is particularly important when you use nested tables.

SAP

You can define internal tables either with (addition WITH HEADER LINE) or without header lines. An internal table with a header line consists of a work area (header line) and the actual table body. You address both objects using the same name.

BC401


Example for Using an Internal Table with a Header Line DATA itab1 TYPE TABLE OF i WITH HEADER LINE. DATA itab2 LIKE itab1.

itab1

= itab2.

" method_name .... When calling an instance method from within another instance method, you can omit the instance name ref. The method is automatically executed for the current object.


139

Unit 2: Introduction to Object-Oriented Programming

BC401

Use

Partner

Only

Internal

Figure 83: Calling Static Methods – Syntax

SAP

Like static attributes, static methods are addressed with their class name, since they do not need instances.

Use

Only

Internal

Partner

As with instance methods, when you are calling a static method from within the class, you can omit the classname. Otherwise, the same rules apply here as for calling an instance method.

SAP

Static methods (also referred to as class methods) are called using CALL METHOD classname=>method_name ....

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Lesson: Fundamental Object-Oriented Syntax Elements

Use

Partner

Only

Internal

Figure 84: Functional Methods

SAP Use

•

• • •

08-03-2004

Logical expressions (IF, ELSEIF, WHILE, CHECK, WAIT) Case conditions (CASE, WHEN) Arithmetic expressions and bit expressions (COMPUTE) Sources of values as a local copy (MOVE) Search clauses for internal tables, assuming that the operand is not a component of the table row (LOOP AT ... WHERE).


Only

Internal

•

Partner

Functional methods can be called directly within various expressions:

SAP

Methods that have a RETURNING parameter are described as functional methods. This means that they can have neither an EXPORTING nor a CHANGING parameter. The RETURNING parameter must always be passed using the VALUE addition, that is, by value as a local copy.

141


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Use

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Only

Internal

Figure 85: Functional Methods – Examples

SAP Use

DATA number TYPE i. ...

Internal

CALL METHOD lcl_vehicle=>get_n_o_vehicles

Partner

The second example shows the call of a functional static method in the short form: The NUMBER data object is the actual parameter for the method’s RETURNING parameter. The detailed syntax is as follows:

SAP

In the first of these examples, two calls of functional instance methods represent the two addends of an addition.

RECEIVING re_count = number.

Only

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Internal

Partner

Only

BC401

You access public attributes from outside a class the same way as method calls: Static attributes are accessed using classname=>static_attribute. Instance attributes are accessed with ref->instance_attribute.

Use

Constructors

SAP

SAP

Figure 86: Accessing Public Attributes

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Only

Internal

Partner

There are two types of methods in ABAP Objects. They are generally not called explicitly with CALL METHOD (or the relevant short form), but are called implicitly. Constructors are the first type of method.

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Internal

Figure 87: (Instance) Constructor

SAP

SAP

The constructor is a special instance method in a class and is always named CONSTRUCTOR. This abbreviated term actually means the instance constructor.

Only

Internal

Use

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The constructor is automatically called at runtime with the CREATE OBJECT statement. Always consider the following points when you define constructors: • • •

Only

•

(The corresponding comments in the SAP Library and the menu paths outside of the ABAP Workbench are only contained in internal system calls.)

Use

Partner

Note: There is no destructor in ABAP Objects. That is, there is no instance method that is automatically called from the memory immediately before the object is deleted.

Internal

•

Each class can have no more than one (instance) constructor The constructor must be defined in the public area The constructor’s signature can only have importing parameters and exceptions When exceptions are raised in the constructor, instances are not created, so no main memory space is occupied Except for one exceptional case, you cannot normally call the constructor explicitly

SAP

SAP Only

Internal

Use

Partner

Figure 88: Constructor – Example

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BC401

For example, a constructor is necessary when, after the instantiation of a class: • • • •

You need to allocate resources You need to initialize attributes that cannot be covered by the VALUE addition to the DATA statement You need to modify static attributes You need to send messages containing the information that a new object was created

Use

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Internal

Internal

• • • •

146

Creating an instance of this class (CREATE OBJECT) Accessing a static attribute of this class Calling a static method of this class Registering an event handler method for an event in this class


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The static constructor is a special static method in a class and is always named CLASS_CONSTRUCTOR. It is executed no more than once per program (and class). The static constructor is called automatically before the class is first accessed, but before any of the following actions are executed for the first time:

Partner

Use

SAP

SAP

Figure 89: Example of a Static Constructor

BC401


Always consider the following points when you define static constructors: • • • •

Each class has no more than one static constructor The static constructor must be defined in the public area The constructor’s signature cannot have importing parameters or exceptions The static constructor cannot be called explicitly

Only

Use

Partner

In some cases, you need to have a self-reference available. In ABAP Objects, self-references are always predefined, but they are only useful in certain contexts and only there are they syntactically available.

Internal

Self-Reference

SAP

SAP

You can address an object itself by using the predefined reference variable ME within its instance methods . Generally, you do not need to use the prefix me-> in such cases, but you may use it to improve readability. However, it is required when you want to show a distinction between local data objects and instance attributes with the same name.

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Figure 90: Self-Reference


BC401

The following case shows another important use: When a “foreign” method is called, a client object is to export a reference to itself. ME can then be used as an actual parameter with EXPORTING or CHANGING.

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SAP

SAP Only

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Exercise 6: Local Classes Exercise Objectives

Only

Task 1:

You are a developer for an airline corporation that owns several airline carriers. Start to develop an object-oriented program that can manage the airline carriers and their airlines.

Use

Create a new program. 1.

Create an executable program without a TOP include.

SAP

(Where ## is your two-digit group number).

Use

Program name: ZBC401_##_AIRPLANE

Internal


Task 2:

Partner

Create an include program and include it in your ZBC401_##_MAIN main program.

SAP

Program name: ZBC401_##_MAIN

2.

Internal

Business Example

Partner

After completing this exercise, you will be able to: • Declare local classes • Define attributes • Define and implement methods

Declare a class for airplanes.

2.

Within your include program, declare the local class LCL_AIRPLANE. Define the two private instance attributes NAME (name of airplane), data type STRING PLANETYPE (type of airplane), data type SAPLANE-PLANETYPE and the private static attribute N_O_AIRPLANES (instance counter), data type I. Continued on next page

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1.


3.

BC401

Define the public instance method SET_ATTRIBUTES for setting the private instance attributes. Your signature should consist of two suitable import parameters that are defined compatibly to the two attributes. Implement the method in such a way that the two instance attributes are set. Define the public instance method DISPLAY_ATTRIBUTES for displaying the private instance attributes.

Hint: Use the statement TYPE-POOLS icon. to do this.

SAP

Define the public static method DISPLAY_N_O_AIRPLANES to display the private static attribute.

Note: So far, your class does not have a mechanism that ensures that the instance counter is increased each time an object is created. It is up to you to decide if you want to leave this out for now, of if you want to temporarily control the incrementation using the SET_ATTRIBUTES method.

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Internal

Implement the method in such a way that the value of the static attributes is output in the ABAP list.

Partner

Use

5.

SAP

Note: Strictly speaking, to adhere to the delegation principle, the reading of the attribute values and their output should not be implemented in the same method. However, do it here anyway because of time constraints.

Use

Partner

Implement the method in such a way that the values of the two instance attributes are output as an ABAP list. You can also output icons if the ICON type group is loaded.

Internal

Only

4.

BC401


Solution 6: Local Classes Task 1: Create a new program. 1.

Create an executable program without a TOP include. Program name: ZBC401_##_MAIN

Only

a)


Partner

Model solution: SAPBC401_AIRS_MAIN_A 2.

Create an include program and include it in your ZBC401_##_MAIN main program.

Use

Program name: ZBC401_##_AIRPLANE (Where ## is your two-digit group number). Carry out this step in the usual manner. Additional information is available in the SAP Library. Model solution: SAPBC401_AIRS_A See the source code extract from the model solution

Task 2: Declare a class for airplanes. Within your include program, declare the local class LCL_AIRPLANE. a) 2.


Define the two private instance attributes

Only

Internal

1.

NAME (name of airplane), data type STRING PLANETYPE (type of airplane), data type SAPLANE-PLANETYPE and the private static attribute N_O_AIRPLANES (instance counter), data type I. a)



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b)

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SAP

a)

Internal


151


3.

BC401

Define the public instance method SET_ATTRIBUTES for setting the private instance attributes. Your signature should consist of two suitable import parameters that are defined compatibly to the two attributes. Implement the method in such a way that the two instance attributes are set.

4.


Define the public instance method DISPLAY_ATTRIBUTES for displaying the private instance attributes.

Hint: Use the statement TYPE-POOLS icon. to do this.

SAP Use

Define the public static method DISPLAY_N_O_AIRPLANES to display the private static attribute. Implement the method in such a way that the value of the static attributes is output in the ABAP list. Note: So far, your class does not have a mechanism that ensures that the instance counter is increased each time an object is created. It is up to you to decide if you want to leave this out for now, of if you want to temporarily control the incrementation using the SET_ATTRIBUTES method. a)



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Internal

5.


Partner

a)

SAP

Note: Strictly speaking, to adhere to the delegation principle, the reading of the attribute values and their output should not be implemented in the same method. However, do it here anyway because of time constraints.

Use

Partner

Implement the method in such a way that the values of the two instance attributes are output as an ABAP list. You can also output icons if the ICON type group is loaded.

Internal

Only

a)

BC401



SAPBC401_AIRS_MAIN_A

Only

SAPBC401_AIRS_A

sapbc401_airs_main_a.

Internal

TYPE-POOLS icon.

Partner

REPORT

INCLUDE sapbc401_airs_a.

*&---------------------------------------------------------------------* Include

SAPBC401_AIRS_A

*

Use

*&

*&---------------------------------------------------------------------* *------------------------------------------------------------------* *

CLASS lcl_airplane DEFINITION

*

SAP

SAP

*------------------------------------------------------------------* CLASS lcl_airplane DEFINITION.

PUBLIC SECTION.

Use

Partner

"-------------------------------CONSTANTS: pos_1 TYPE i VALUE 30.

METHODS: set_attributes IMPORTING

Internal

im_name

TYPE string

im_planetype TYPE saplane-planetype, display_attributes.

Only

CLASS-METHODS: display_n_o_airplanes.

PRIVATE SECTION. "---------------------------------DATA: name

TYPE string,

planetype TYPE saplane-planetype.

CLASS-DATA: n_o_airplanes TYPE i.


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BC401

"lcl_airplane DEFINITION

ENDCLASS.

*------------------------------------------------------------------* *

CLASS lcl_airplane IMPLEMENTATION

*

*------------------------------------------------------------------* CLASS lcl_airplane IMPLEMENTATION.

name

= im_name.

planetype

= im_planetype.

*

doesn’t make sense so much -

*

only in order to get an effect

*

after calling display_n_o_airplanes:

Internal

Only

METHOD set_attributes.

Partner

n_o_airplanes = n_o_airplanes + 1. "set_attributes

ENDMETHOD.

Use

METHOD display_attributes. WRITE: / icon_ws_plane AS ICON, / ’Name des Flugzeugs:’(001), AT pos_1 name, / ’Flugzeugtyp’(002), AT pos_1 planetype.

SAP

SAP

"display_attributes

ENDMETHOD.

METHOD display_n_o_airplanes. WRITE: /, / ’Gesamtzahl der Flugzeuge’(ca1), AT pos_1 n_o_airplanes LEFT-JUSTIFIED, /.

Use

"display_n_o_airplanes "lcl_airplane IMPLEMENTATION

Only

Internal

ENDCLASS.

Partner

ENDMETHOD.

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Exercise 7: Objects Exercise Objectives

Business Example

Task 1: Define reference variables. 1.

Complete your ZBC401_##_MAIN program or copy the sample solution from the previous exercise.

SAP

Define an internal table for buffering references to instances of the class LCL_AIRPLANE.

Task 2:

08-03-2004

1.

Create several instances of the local class LCL_AIRPLANE and buffer their references into the internal table.

2.

Follow the execution of the program in the ABAP Debugger.


Only

Internal

Create airplane objects.

Partner

Use

2.

SAP

Define a reference variable for the instances of your class LCL_AIRPLANE.

Use

Partner

Create instances of your airplane type and ensure that their addresses are not lost.

Internal

Only

After completing this exercise, you will be able to: • Define reference variables • Instantiate objects • Process object references using an internal table

155


BC401

Solution 7: Objects Task 1: Define reference variables. 1.


Only

a) b)

Define an internal table for buffering references to instances of the class LCL_AIRPLANE. a)


Use

Partner

2.

Model solution: SAPBC401_AIRS_MAIN_B See the source code extract from the model solution

Task 2: Create airplane objects.

SAP

Create several instances of the local class LCL_AIRPLANE and buffer their references into the internal table. a)


SAP

1.

Internal

Define a reference variable for the instances of your class LCL_AIRPLANE.

Only

Internal

Use

Partner


156


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2.

Follow the execution of the program in the ABAP Debugger. a)



Only

REPORT

Internal

SAPBC401_AIRS_MAIN_B sapbc401_airs_main_b.

Partner

TYPE-POOLS icon. INCLUDE sapbc401_airs_a.

Use

DATA: r_plane TYPE REF TO lcl_airplane,

SAP

SAP

plane_list TYPE TABLE OF REF TO lcl_airplane.

START-OF-SELECTION. *##############################

Partner

Use

CREATE OBJECT r_plane. APPEND r_plane TO plane_list.

CREATE OBJECT r_plane.

Internal

APPEND r_plane TO plane_list.


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APPEND r_plane TO plane_list.

157


BC401

Use

Partner

Only

Internal

SAP

SAP Only

Internal

Use

Partner

158


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BC401


Exercise 8: Method Calls Exercise Objectives

Business Example

Task 1: Call the methods of your class. 1.


SAP Use Internal

Use the SET_ATTRIBUTES method to set the attributes for all objects already created. Choose a unique name for the airplanes. When you are assigning airplane types, use the information in the SAPLANE table as a guide (for example, ’747-400’). Also use at least one invalid airplane type.

3.

Display the attribute values in the ABAP list using the DISPLAY_ATTRIBUTES method.

Only

2.

Task 2: Add a functional method to your class. 1.

In your class, define the public static functional method GET_N_O_AIRPLANES. The signature must only consist of the result parameter RE_COUNT, which must be a whole number. Continued on next page

08-03-2004


Partner

Caution: For reasons explained in the first exercise, you may not notice any effects at the moment.

SAP

Call the static method DISPLAY_N_O_AIRPLANES twice: Once before and once after the instantiations.

Use

Partner

You need to fill the attributes of the “empty” airplane objects with suitable values.

Internal

Only

After completing this exercise, you will be able to: • Call non-functional methods • Define functional methods • Call functional methods:

159


2.

BC401

Call this method instead of DISPLAY_N_O_AIRPLANES and output the value to the ABAP list. Note: This means that you have followed the delegation principle.

Use

Partner

Only

Internal

SAP

SAP Only

Internal

Use

Partner

160


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Solution 8: Method Calls Task 1: Call the methods of your class. 1.


Only

a) b)

Use the SET_ATTRIBUTES method to set the attributes for all objects already created. Choose a unique name for the airplanes. When you are assigning airplane types, use the information in the SAPLANE table as a guide (for example, ’747-400’). Also use at least one invalid airplane type. a)

Display the attribute values in the ABAP list using the DISPLAY_ATTRIBUTES method. a)

Partner

Use

3.



Add a functional method to your class. In your class, define the public static functional method GET_N_O_AIRPLANES. The signature must only consist of the result parameter RE_COUNT, which must be a whole number. a) 2.


Call this method instead of DISPLAY_N_O_AIRPLANES and output the value to the ABAP list. Note: This means that you have followed the delegation principle. a)


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161

Only

Internal

Task 2: 1.

SAP

SAP

2.

Model solution: SAPBC401_AIRS_MAIN_C See the source code extract from the model solution

Use

Partner

Caution: For reasons explained in the first exercise, you may not notice any effects at the moment.

Internal

Call the static method DISPLAY_N_O_AIRPLANES twice: Once before and once after the instantiations.


BC401


SAPBC401_AIRS_MAIN_C REPORT

sapbc401_airs_main_c.

Internal

Only

TYPE-POOLS icon.

INCLUDE sapbc401_airs_c. DATA: r_plane TYPE REF TO lcl_airplane, plane_list TYPE TABLE OF REF TO lcl_airplane,

Use

Partner

count TYPE i.

START-OF-SELECTION.

SAP

SAP

*##############################

lcl_airplane=>display_n_o_airplanes( ).


Use

Partner

APPEND r_plane TO plane_list. r_plane->set_attributes( im_name = ’LH Berlin’ im_planetype = ’A321’ ).

Internal

CREATE OBJECT r_plane. APPEND r_plane TO plane_list. r_plane->set_attributes( im_name = ’AA New York’ im_planetype = ’747-400’ ).

Only

CREATE OBJECT r_plane. APPEND r_plane TO plane_list. r_plane->set_attributes( im_name = ’US Hercules’ im_planetype = ’747-500’ ).

LOOP AT plane_list INTO r_plane. r_plane->display_attributes( ). ENDLOOP.


162


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* long syntax for functional call: * CALL METHOD lcl_airplane=>get_n_o_airplanes * *

RECEIVING re_count = count.

* a little bit shorter:

Internal

Only

* lcl_airplane=>get_n_o_airplanes( RECEIVING re_count = count ). * the shortest syntax for functional call: count = lcl_airplane=>get_n_o_airplanes( ).

SKIP 2.

Partner

WRITE: / ’Gesamtzahl der Flugzeuge’(ca1), count.

Use

SAPBC401_AIRS_C *&

Include

*&

Show functional static method get_n_o_airplanes

SAPBC401_AIRS_C

* *

SAP

SAP

*&---------------------------------------------------------------------*

*&---------------------------------------------------------------------* *------------------------------------------------------------------* *


*

*------------------------------------------------------------------*

Partner

Use

CLASS lcl_airplane DEFINITION.

PUBLIC SECTION. "--------------------------------

Internal

CONSTANTS: pos_1 TYPE i VALUE 30. METHODS: set_attributes IMPORTING TYPE string

Only

im_name


CLASS-METHODS: display_n_o_airplanes, get_n_o_airplanes RETURNING value(re_count) TYPE i.

PRIVATE SECTION. "---------------------------------DATA: name

TYPE string,


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BC401

planetype TYPE saplane-planetype. CLASS-DATA: n_o_airplanes TYPE i.

ENDCLASS.


*------------------------------------------------------------------* *


*

Internal

Only


Partner

METHOD set_attributes. name

= im_name.

planetype

= im_planetype.

n_o_airplanes = n_o_airplanes + 1. ENDMETHOD.

"set_attributes

Use

METHOD display_attributes. WRITE: / icon_ws_plane AS ICON, / ’Name des Flugzeugs:’(001), AT pos_1 name,

SAP

ENDMETHOD.

SAP

/ ’Flugzeugtyp’(002), AT pos_1 planetype. "display_attributes

METHOD display_n_o_airplanes. WRITE: /, / ’Gesamtzahl der Flugzeuge’(ca1),

Partner

Use

AT pos_1 n_o_airplanes LEFT-JUSTIFIED, /. ENDMETHOD.

"display_n_o_airplanes

METHOD get_n_o_airplanes.

ENDCLASS.

164

"get_n_o_airplanes

Only

Internal

re_count = n_o_airplanes. ENDMETHOD.

"lcl_airplane IMPLEMENTATION


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BC401


Exercise 9: Constructors Exercise Objectives

Only

Task 1:

Make your program more realistic: The airplane objects receive their attributes as soon as they are created.

Internal

Business Example

Partner

After completing this exercise, you will be able to: • Define and implement instance constructors • Create instances of classes that contain an instance constructor

Define an instance constructor. Complete your ZBC401_##_MAIN program or copy the sample solution from the previous exercise. (Where ## is your two-digit group number).

SAP

Implement it so that the two instance attributes are set and the instance counter N_O_AIRPLANES is increased by one.

Use

If you previously used the SET_ATTRIBUTES method to increase the instance counter, remove the relevant statement from the method now.

Task 2:

08-03-2004

1.

Your CREATE OBJECT statements from the previous exercise should now be syntactically incorrect. Adapt and correct them.

2.

If necessary, remove the calls of the SET_ATTRIBUTES method.

3.



165

Only

Internal

Create airplane objects.

Partner

2.

SAP

Define a reference variable with a suitable signature for the instances of your class LCL_AIRPLANE.

Use

1.


BC401

Solution 9: Constructors Task 1: Define an instance constructor. 1.

Complete your ZBC401_##_MAIN program or copy the sample solution from the previous exercise. (Where ## is your two-digit group number).

Only

Implement it so that the two instance attributes are set and the instance counter N_O_AIRPLANES is increased by one.

2.

Model solution: SAPBC401_AIRS_MAIN_D See the source code extract from the model solution

If you previously used the SET_ATTRIBUTES method to increase the instance counter, remove the relevant statement from the method now. a)


SAP

Create airplane objects. Your CREATE OBJECT statements from the previous exercise should now be syntactically incorrect. Adapt and correct them. a) 2.

If necessary, remove the calls of the SET_ATTRIBUTES method. See the source code extract from the model solution




SAPBC401_AIRS_MAIN_D REPORT

sapbc401_airs_main_d.


166


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Only

Internal

a) 3.


Partner

Use

1.

SAP

Task 2:

Use

Partner

a) b)

Internal

Define a reference variable with a suitable signature for the instances of your class LCL_AIRPLANE.

BC401


TYPE-POOLS icon. INCLUDE sapbc401_airs_d.


Internal

Only

plane_list TYPE TABLE OF REF TO lcl_airplane.


Partner


CREATE OBJECT r_plane EXPORTING im_name = ’LH Berlin’

Use

im_planetype = ’A321’. APPEND r_plane TO plane_list.

SAP

SAP

r_plane->display_attributes( ).

CREATE OBJECT r_plane EXPORTING im_name = ’AA New York’ im_planetype = ’747-400’.

Partner

Use

APPEND r_plane TO plane_list. r_plane->display_attributes( ).

CREATE OBJECT r_plane EXPORTING im_name = ’US Hercules’

Internal

im_planetype = ’747-500’. APPEND r_plane TO plane_list.

Only

r_plane->display_attributes( ).


SAPBC401_AIRS_D *&---------------------------------------------------------------------* *&

Include

SAPBC401_AIRS_D

*

*&---------------------------------------------------------------------*


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BC401

*------------------------------------------------------------------* *


*

*------------------------------------------------------------------* CLASS lcl_airplane DEFINITION. PUBLIC SECTION. "-------------------------------CONSTANTS: pos_1 TYPE i VALUE 30.

im_name

Internal

Only

METHODS: constructor IMPORTING TYPE string


Partner

CLASS-METHODS: display_n_o_airplanes. PRIVATE SECTION. DATA: name

Use

"---------------------------------TYPE string,


SAP

ENDCLASS.

SAP

CLASS-DATA: n_o_airplanes TYPE i. "lcl_airplane DEFINITION

*------------------------------------------------------------------* *


*

Partner

Use


Internal

METHOD constructor. name

= im_name.

planetype

= im_planetype.

n_o_airplanes = n_o_airplanes + 1. "constructor

ENDMETHOD.

Only

METHOD display_attributes. WRITE: / icon_ws_plane AS ICON, / ’Name des Flugzeugs’(001), AT pos_1 name, / ’Type of airplane: ’(002), AT pos_1 planetype. ENDMETHOD.

"display_attributes

METHOD display_n_o_airplanes. WRITE: /, / ’Number of airplanes: ’(ca1), AT pos_1 n_o_airplanes LEFT-JUSTIFIED, /.


168


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BC401


ENDMETHOD. ENDCLASS.

"display_n_o_airplanes "lcl_airplane IMPLEMENTATION

Use

Partner

Only

Internal

SAP

SAP Only

Internal

Use

Partner

08-03-2004


169


BC401

Use

Partner

Only

Internal

SAP

SAP Only

Internal

Use

Partner

170


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BC401


Exercise 10: Private Methods Exercise Objectives

Only

Declare another method. 1.


SAP Use

Implement the method in such a way that the values for the export parameters can be determined by single-record access to the database table SAPLANE. If no values for that airplane type exist in that table, the following standard values should be used for the time being: Weight: 100,000, tank capacity: 10,000 Note: Strictly speaking, the correct unit of measurements should also be selected and exported. However, time constrains mean that you do not need to do it in this exercise.


08-03-2004


171

Only

Internal

2.

Partner

The signature must consist of an import parameter for the airplane type and two export parameters for the weight and the tank capacity. Use the transparent table SAPLANE as a guide for specifying the types of these formal parameters.

SAP

Within the class LCL_AIRPLANE, define the private instance method GET_TECHNICAL_ATTRIBUTES.

Use

Task 1:

An airplane object should be able to display additional technical data on request, so that a complete business application object is displayed for the user.

Internal

Business Example

Partner

After completing this exercise, you will be able to: • Use the delegation principle • Realize business application objects based on database contents


BC401

Task 2: The method DISPLAY_ATTRIBUTES should only be responsible for displaying the data. Call your method again to delegate the retrieval of the technical data.

2.


3.

Are there any alternative solutions that fulfill the same purpose, but still adhere to the delegation principle? What are they?

Use

Partner

1.

Internal

Only

Call the method.

SAP

SAP Only

Internal

Use

Partner

172


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BC401


Solution 10: Private Methods Task 1: Declare another method. 1.


Only

a) b) 2.

Model solution: SAPBC401_AIRS_MAIN_E See the source code extract from the model solution

Implement the method in such a way that the values for the export parameters can be determined by single-record access to the database table SAPLANE.

SAP

SAP

If no values for that airplane type exist in that table, the following standard values should be used for the time being:


Task 2: Call the method. 1.

The method DISPLAY_ATTRIBUTES should only be responsible for displaying the data. Call your method again to delegate the retrieval of the technical data. a)



08-03-2004


173

Only

Internal

Note: Strictly speaking, the correct unit of measurements should also be selected and exported. However, time constrains mean that you do not need to do it in this exercise.

Partner

Use

Weight: 100,000, tank capacity: 10,000

a)

Use

Partner

The signature must consist of an import parameter for the airplane type and two export parameters for the weight and the tank capacity. Use the transparent table SAPLANE as a guide for specifying the types of these formal parameters.

Internal

Within the class LCL_AIRPLANE, define the private instance method GET_TECHNICAL_ATTRIBUTES.


2.


3.

BC401


Are there any alternative solutions that fulfill the same purpose, but still adhere to the delegation principle? What are they? Answer:

Only

Not using the import parameter GET_TECHNICAL_ATTRIBUTES is an instance method. Therefore, during single-record access, the private attribute for the airplane type could be used in the WHERE clause. Private static method while preserving the signature This way the method could be seen as a central “data retrieval service” for all instances of the class.

•

Not using the method at all Instead, you could use other suitable private attributes, which the constructor could fill with values from the database table.

SAP

SAPBC401_AIRS_E

Source code extract:

*&---------------------------------------------------------------------* Include

SAPBC401_AIRS_E

*

Internal

*&---------------------------------------------------------------------* *------------------------------------------------------------------* *


*

Only

*------------------------------------------------------------------* CLASS lcl_airplane DEFINITION. PUBLIC SECTION. "-------------------------------CONSTANTS: pos_1 TYPE i VALUE 30.

METHODS: constructor IMPORTING im_name

TYPE string

im_planetype TYPE saplane-planetype,


174


Partner

Use

SAP

Result

*&

Use

Partner

•

Internal

•

08-03-2004

BC401


display_attributes. CLASS-METHODS: display_n_o_airplanes.

PRIVATE SECTION. "----------------------------------

IMPORTING im_type

TYPE saplane-planetype

EXPORTING ex_weight

TYPE s_plan_wei

ex_tankcap

DATA: name

Internal

Only

METHODS: get_technical_attributes

TYPE s_capacity.

TYPE string,

Partner



Use

ENDCLASS.

*------------------------------------------------------------------* *


*

SAP

SAP


name

= im_name.

planetype

= im_planetype.

Partner

Use

METHOD constructor.


"constructor

Internal

METHOD display_attributes. DATA: weight TYPE saplane-weight, cap TYPE saplane-tankcap.

Only

WRITE: / icon_ws_plane AS ICON, / ’Name des Flugzeugs’(001), AT pos_1 name, / ’Type of airplane: ’(002), AT pos_1 planetype. get_technical_attributes( EXPORTING im_type = planetype IMPORTING ex_weight = weight ex_tankcap = cap ). WRITE: / ’Wheight: ’(003), 20 weight, ’Tankcap: ’(004), 60 cap. ENDMETHOD.

"display_attributes


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175


BC401

METHOD display_n_o_airplanes. WRITE: /, / ’Number of airplanes: ’(ca1), AT pos_1 n_o_airplanes LEFT-JUSTIFIED, /. ENDMETHOD.


METHOD get_technical_attributes. SELECT SINGLE weight tankcap FROM saplane INTO (ex_weight, ex_tankcap)

Internal

Only

WHERE planetype = im_type. IF sy-subrc 0. ex_weight = 100000. ex_tankcap = 10000. ENDIF.

Partner

ENDMETHOD.

ENDCLASS.

"get_technical_attributes "lcl_airplane IMPLEMENTATION

Use

SAP

SAP Only

Internal

Use

Partner

176


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Lesson Summary You should now be able to: • Define classes • Generate and delete objects • Access attributes • Call methods

Only

Use

Partner


Internal

Related Information

SAP

SAP Only

Internal

Use

Partner

08-03-2004


177

Unit Summary

BC401

Unit Summary

Only

Use

Partner

Internal

You should now be able to: • Explain the differences between procedural and object-oriented programming models • List the advantages of the object-oriented programming model • Name the most important diagram types in UML • Create class diagrams • Create sequence diagrams • Define classes • Generate and delete objects • Access attributes • Call methods

SAP

SAP Only

Internal

Use

Partner

178


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BC401

Test Your Knowledge

Test Your Knowledge 1.

The object-oriented programming model was developed considerably later than the procedural one. It offers more possibilities to solve problems that previously could not be solved with purely procedural programming languages. Determine whether this statement is true or false.

Only

3.

What does encapsulation mean?

4.

In ABAP Objects, what is meant by the term class?

5.

What is the difference between a class’s static components and its instance components?


Internal

Only

08-03-2004

Partner

Use

SAP

SAP

What does multiple instantiation mean?

Use

2.

Partner

True False

Internal

□ □

179

Test Your Knowledge

BC401

6.

In ABAP Objects, what is meant by the term constructor?

7.

You are defining a class. Must you always also define a constructor?

Use

Partner

Only

Internal

SAP

SAP Only

Internal

Use

Partner

180


08-03-2004

BC401

Test Your Knowledge

Answers 1.

The object-oriented programming model was developed considerably later than the procedural one. It offers more possibilities to solve problems that previously could not be solved with purely procedural programming languages.

Internal

Only

Answer: False Refer to the relevant section of the lesson. 2.

What does multiple instantiation mean?

Partner

Answer: The ability to create and manage any number of runtime instances for each program context

3.

Use

Refer to the relevant section of the lesson. What does encapsulation mean?

SAP

Refer to the relevant section of the lesson.

Use

In ABAP Objects, what is meant by the term class?

Internal

Answer: A class is the technical description of identical objects. Among other things, it can contain attribute and method definitions. It usually also contains the methods’ implementations. Refer to the relevant section of the lesson.

Partner

4.

SAP

Answer: Gathering data and functions into reusable units from which users can only call certain functions and cannot access the data directly.

Only

08-03-2004


181

Test Your Knowledge

5.

BC401

What is the difference between a class’s static components and its instance components?

Only

Refer to the relevant section of the lesson. In ABAP Objects, what is meant by the term constructor? Answer: A class’s constructor is a special method and is always named CONSTRUCTOR. It is normally only called by the runtime system, whenever an object of this class is created using CREATE OBJECT. Therefore, it is referred to more specifically as the instance constructor. Refer to the relevant section of the lesson.

SAP

You are defining a class. Must you always also define a constructor? Answer: No

Only

Internal

Use

Partner


SAP

7.

Use

Partner

6.

Internal

Answer: You have to access static components through the class. That means they can exist only once per program and class in the memory. An object must be instantiated to access them. You have to access instance components through the objects of the class. That means, they can exist any number of times per program and class in the memory.

182


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Unit 3 Only

Unit Overview

Partner SAP

Unit Objectives

Use Internal

08-03-2004

Define inheritance relationships between classes Redefine methods Create narrowing cast assignments Create widening cast assignments Explain the concept of polymorphism with reference to interfaces Use cast assignments with inheritance to make generic calls Define and implement interfaces Implement interface methods Use interface references to make narrowing cast assignments Use interface references to make widening cast assignments Explain the term polymorphism with reference to interfaces Use cast assignments with interfaces to make generic calls Define and trigger events Handle events


Only

• • • • • • • • • • • • • •

Partner

After completing this unit, you will be able to:

SAP

Every concept exists for a specific reason. It is important that you understand them all without exception so that you can use each of them effectively later on. You can only capitalize on the strengths of object-oriented programming if you use all of the concepts in the intended manner.

Use

This unit deals with the basic programming techniques common to all object-oriented languages. As far as these concepts are concerned, the only difference between ABAP Objects and other languages like Java or C++ is the syntax.

Internal

Object-Oriented Concepts and Programming Techniques

183

Unit 3: Object-Oriented Concepts and Programming Techniques

• •

BC401

Register and deregister event handling Explain the key differences between explicit method calls and event-controlled method calls

Unit Contents

Only

Use

Partner

Internal

Lesson: Inheritance and Casting ................................................. 185 Exercise 11: Class Hierarchies ............................................... 205 Exercise 12: Polymorphism ................................................... 215 Exercise 13: Aggregation and Generic Calls ............................... 219 Lesson: Interfaces and Casting ................................................... 226 Exercise 14: Interface Implementation ...................................... 241 Exercise 15: Aggregation, Generic Calls, and Polymorphism ............ 255 Lesson: Events...................................................................... 263 Exercise 16: Events in Superclasses ........................................ 273 Exercise 17: Events in Interfaces (optional) ................................ 287

SAP

SAP Only

Internal

Use

Partner

184


08-03-2004

BC401

Lesson: Inheritance and Casting

Lesson: Inheritance and Casting Lesson Overview

Internal

Only

In this lesson you will learn how to create class hierarchies using ABAP Objects. The first step will be to program the relevant relationship types that were devised in the modeling process. Then you will learn to identify a number of advantageous programming possibilities that inheritance provides.

Lesson Objectives After completing this lesson, you will be able to:

Partner SAP Internal

08-03-2004


185

Only

Specialization (UML) is a relationship in which one class (the subclass) inherits all the main characteristics of another class (the superclass). The subclass can also add new components (attributes, methods, and so on) and replace the implementations with inherited methods. In the latter case, the method name in the UML diagram is renamed within the subclass.

Partner

Realization of Generalization/Specialization Relationships Using Iheritance

You want to implement generalization/specialization relationships from your model in ABAP Objects.

SAP

Business Example

Use

Define inheritance relationships between classes Redefine methods Create narrowing cast assignments Create widening cast assignments Explain the concept of polymorphism with reference to interfaces Use cast assignments with inheritance to make generic calls

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• • • • • •


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Reversing the point of view is referred to as generalization.

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Specialization is often described as an “is a” relationship. In this example, you would say: “A truck is a (specific) vehicle.”

SAP

Inheritance is an implementation relationship that emphasizes similarities of the classes. In the example above, the similarities of classes LCL_CAR, LCL_TRUCK, and LCL_BUS are extracted to a superclass, LCL_VEHICLE. Therefore, the components they have in common are only defined and implemented in the superclass. They also exist in all subclasses.

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Figure 91: Example of Generalization/Specialization

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Figure 92: Characteristics of Generalization/Specialization

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When you develop additional subclasses, you often have to adapt the superclass, too. Sometimes the creation of a subclass leads to additional requirements for the superclass, for example, when a subclass requires certain protected components or when the details of a superclass’s implementation are required to change the method implementations in subclasses. The developer of a (super)class cannot normally predict everything that the subclasses will later require from the superclass.

Partner

You need exact knowledge of the implementation of the superclass to decide whether the inherited components from the superclass are sufficient for the subclass or if they need to be extended. Generalization/specialization therefore provides very strong links between the superclass and the subclass.

SAP

If generalization/specialization is used properly, it provides a significantly better structure for your software, as common components only need to be stored once centrally (in the superclass). That is, subsequent changes are then automatically applied to subclasses. Therefore, you must not alter the semantics when you change a superclass.

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Figure 93: Inheritance – Syntax


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Inheritance is a “one-sided relationship”: subclasses know their direct superclasses, but (super)classes do not know their subclasses. In this example, the subclass also contains the ESTIMATE_FUEL method. The subclass also defines the GET_CARGO method.

SAP

Inheritance should be used to implement generalization and specialization relationships. A superclass is a generalization of its subclasses. The subclasses are in turn different specializations of their superclass. Only additions or changes are permitted in ABAP Objects, that is, in a subclass you can „never take something away from a superclass".

Use

In ABAP Objects, an inheritance relationship is defined for a subclass using the INHERITING FROM addition, followed by the superclass that is directly above the subclass. Inheritance hierarchies of varying complexity arise when this superclass inherits from another superclass above it. On the other hand, there is no multiple inheritance in ABAP Objects. That is, only one superclass can be specified directly above a class. However, you can use interfaces in ABAP Objects to simulate multiple inheritance.

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Within the redefined method’s implementation part, you can use the predefined prefix super->... to access components in the superclass directly above where you are working. You often need to do this when redefining a method to call the original method of the superclass.

Partner

When you use the REDEFINITION addition, you must specify a (new) implementation part for the inherited method. As the signature may not be changed, you do not need to define the method parameters and exceptions again.

SAP

Redefinition is when the implementation of an inherited instance method is changed for the subclass, without changing the signature. At the same time, the visibility section for the superclass must remain the same. (Therefore, redefinition is not possible without the PRIVATE SECTION.)

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Figure 94: Redefining Methods


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Figure 95: Preserving Semantics During Redefinition

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In this example, both redefined methods calculate the return code in different ways. The important point is that the method’s semantics stay the same.

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Figure 96: “Overloading” of the Constructor

Generally, redefining by the constructor would not be useful. Either the superclass’s constructor can be used without any need to change it or the subclass has been expanded and other parameters are now required in

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the constructor’s signature. Therefore, in ABAP Objects inheritance, the constructor can only be “overloaded,” in the sense that both the signature and the implementation part can be adapted.

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Unlike instance constructors, the static constructor in the superclass is called automatically. That is, the runtime system automatically ensures that the static constructors of all its superclasses have already been executed before the static constructor in a particular class is executed.

Internal

The constructor of the superclass must be called within the constructor of the subclass. This is because of the specialization relationship: If a constructor was defined in the superclass, it contains implementations that will always be executed when an object is created in this superclass or its subclasses. However, only if the subclass’s constructor was not overloaded, can the runtime system ensure this automatically. In most cases, supplying consistent private attributes from the superclass is another prerequisite for calling the superclass constructor.

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Figure 97: Rules for Calling the Constructor

If a subclass has not overloaded its instance constructor, the constructor is left unchanged and is adopted by the superclass. Therefore, the implementation is executed from the superclass.

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When defining local classes in ABAP Objects, you must follow the syntactical sequence of PUBLIC SECTION, PROTECTED SECTION, PRIVATE SECTION.

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Inheritance provides an extension of the visibility concept: There are protected components (PROTECTED SECTION). The visibility of these components is a “grey area” between public and private. Protected components are visible to all subclasses and the class itself.

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Figure 98: Inheritance and Visibility

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Figure 99: Protected vs. Private Section

Using the private visibility section, you can change superclasses without the need to know the subclasses. As long as the changes you make do not affect the sematics, you do not need to adapt the subclasses. This is because they only indirectly access the private components from the superclass.

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In this example, it is possible to access the protected attribute TANK in superclass LCL_VEHICLE directly from its subclass LCL_BUS. On the other hand, the only way to access the MAKE and MODEL attributes from the subclasses of LCL_VEHICLE is to use public methods.

There is only one static component per program context. To summarize:

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The fact that all components of a superclass are available to the subclass is not related to the component’s visibility. A subclass also receives the private components of its superclass. However, these cannot be addressed in the syntax of the subclass. Private components in superclasses can only be addressed indirectly, that is through public or protected methods from the superclass that can access private attributes. These restrictions are necessary to ensure that centralized maintenance is possible.


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Static Components and Inheritance • •

A class that defines a public or protected static attribute shares this attribute with all its subclasses Static methods cannot be redefined

narrowing cast

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Variables of the type “reference to superclass” can also refer to subclass instances at runtime.

Internal

The user can therefore address the subclass instance in the same way as the superclass instance. However, it is restricted to using only the inherited components. In this example, after the assignment, the methods GET_MAKE, GET_COUNT, DISPLAY_ATTRIBUTES, SET_ATTRIBUTES and ESTIMATE_FUEL of the instance LCL_TRUCK can only be accessed using the reference R_VEHICLE.

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If you assign a subclass reference to a superclass reference, this ensures that all components that can be accessed syntactically after the cast assignment are actually available in the instance. The subclass always contains at least the same components as the superclass. After all, the name and the signature of redefined methods are identical.

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Figure 100: Narrowing Cast With Object References

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If there are any restrictions regarding visibility, they are left unchanged. It is not possible to access the specific components from the class LCL_TRUCK of the instance (GET_CARGO in the above example) using the reference R_VEHICLE. The view is thus generally narrowed (at least unchanged). That is why we describe this type of assignment of reference variables as narrowing cast. There is a switch from a view of several components to a view of a few components. The term upcast is also common.

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object_id

In the example, LCL_VEHICLE is the static type of the variable R_VEHICLE. Depending on the cast assignment, the dynamic type is either LCL_BUS or LCL_TRUCK. In the ABAP Debugger, the dynamic type is shown in form of the object display

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Assignments between reference variables are possible whenever the static type of the target variables is more general or equal to the dynamic type of the source variables.

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A reference variable always has two types at runtime: static and dynamic.

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Figure 101: Static and Dynamic Types of References

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In the example shown here, a travel agency (LCL_RENTAL) needs to manage all imaginable kinds of vehicles in one list. This leads to the question of what type should be assigned to the internal table for the references to airplaine instances. You should also assume that the car rental company needs to be able to calculate only the required amount of fuel for all its vehicles. Correspondingly, the ESTIMATE_FUEL method is defined in the superclass LCL_VEHICLE and is redefined in all subclasses.

SAP

A typical use for narrowing cast assignments is to prepare for generic access: A user, who is not at all interested in the finer points of the instances of the subclasses but who simply wants to address the shared components, could use a superclass reference for this access.

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Figure 102: Generic Access After Narrowing Cast Assignments

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Figure 103: Line Type of the Internal Table in the Applied Example

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SAP

When objects of different classes (LCL_BUS, LCL_TRUCK, and LCL_CAR in the above example) are specified as type superclass references (LCL_VEHICLE in the above), they can be stored in an internal table. The shared components of the subclass objects can then be accessed uniformly. For this example, the method ADD_VEHICLE is therefore needed. This copies the references to the vehicle types in this internal table. Its import parameter is already typed as the reference to the superclass.

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Figure 104: Narrowing Cast and Generic Access in the Applied Example

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In this example, the narrowing cast assignment occurs when the vehicle reference is transfered to the formal parameter of the ADD_VEHICLE method. The shared component is generically accessed within the loop around the internal table containing all of the vehicle references: The ESTIMATE_FUEL method was inherited from the LCL_VEHICLE superclass and may have been redefined.

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When an instance receives a message to execute a particular method, the method that implemented the class of this instance is executed. If the class has not been redefined in the method, the implementation from the superclass is executed.

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Which implementation is executed when ESTIMATE_FUEL is called now depends on which object the superclass reference R_VEHICLE currently refers to. The dynamic type and not the static type of the reference variable is used to search for the implementation of a method. Therefore, when r_vehicle->estimate_fuel is called, the implementation is not executed from LCL_VEHICLE (static type of R_VEHICLE) because the method was redefined in all vehicle classes.

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Figure 105: Polymorphism – Generic Access Using the Superclass Reference

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When objects from different classes react differently to the same method calls, this is known as polymorphism. The possibility of polymorphism is one of the main strengths of inheritance: A client can handle different classes uniformly, irrespective of their implementation. The runtime system searches for the right implementation of a method on behalf of the client.

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Polymorphism can be used to write programs that are highly generic, that is, they do not need to be changed significantly if use cases are added. For instance, this would make it very easy to add motor bikes to this example: You would simply have to define a new subclass of LCL_VEHICLE, which you could call LCL_MOTORBIKE. You would also have to redefine the inherited method ESTIMATE_FUEL. Without needing any more changes, your vehicle management system could then work with motorbikes as well and calculate the required fuel levels for them.

SAP

SAP

Using dynamic function modules, you can program generically in ABAP Objects, even without an object-oriented programming model. Compared with polymorphism through inheritance, this means that the source code is less self-explanatory and is more succeptible to errors. For example, the syntax check can only check that the function model is called correctly but not if the internal table contains a valid function module name for each vehicle.

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Figure 106: Generic Calls in the Procedural Programming Model


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Widening Cast Variables of the type “reference to superclass” can also refer to subclass instances at runtime. You may now want to copy such a reference (back) onto a suitable variable of the type “reference to subclass”.

After assigning this type of reference (back) to a subclass reference to the implementing class, clients are no longer limited to inherited components: In the example given here, all components of the LCL_TRUCK instance can be accessed (again) after the assignment using reference R_TRUCK2.

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If you want to assign a superclass reference to a subclass reference, you must use the widening cast assignment operator MOVE ... ?TO ... or its short form ?= . Otherwise, you would get a message stating that it is not certain that all components that can be accessed syntactically after the cast assignment are actually available in the instance. As a rule, the subclass class contains more components than the superclass.

The view is thus widened (at least unchanged). That is why we describe this type of assignment of reference variables as widening cast. There is a switch from a view of a few components to a view of more components. The term downcast is also common.

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Figure 107: Widening Cast With Object References


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In this example, a car rental company (LCL_RENTAL) wants to determine the maximum capacity of its trucks, but it stores all types of vehicle references in an internal table that is typed as LCL_VEHICLE. Therefore, what happens if there is no truck reference in the superclass reference R_VEHICLE at runtime but the widening cast assignment operator tries to copy the reference to the now invalid reference R_TRUCK?

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Internal

A typical use for widening cast assignments is when specific components of instances need to be addressed and their references are kept in variables that are typed on the superclass. A user who is interested in the finer points of the instances of a subclass cannot use the superclass reference for this access because it only allows access to the shared components.

SAP

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Figure 108: Specific Access After Widening Cast Assignments

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This final section does not examine whether or not inheritance should be used as a programming technique over a number of alternatives. As early as the modeling phase, you should be able to see if there is a generalization/specialization relationship between certain classes. If there is, you can use inheritance to represent this in ABAP Objects.

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Using Inheritance

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This exception of error class CX_SY_MOVE_CAST_ERROR can be identified using TRY-ENDTRY and the CATCH statement. Another way of preventing this runtime error would be to use runtime type identification (RTTI) classes. They can be used to determine the dynamic type at runtime and to set a condition for the cast.

SAP

In contrast to the narrowing cast assignment, it is possible that the static type of the target variable (R_TRUCK) is neither more general than nor the same as the dynamic type of the source variable (R_VEHICLE), namely when R_VEHICLE contains bus or sports car references. That is why with this kind of cast, the runtime system checks, before the assignment, whether the current content of the source variable corresponds to the type requirements of the target variable. Otherwise, an exception that can be handled is triggered, and the original value of the target variable remains the same.

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Figure 109: Widening Cast Assignment and Exception Handling in the Application Example


Figure 110: Using Inheritance

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In that case, you need to adhere to the relevant concepts of inheritance. For example, the semantics must be preserved when you redefine methods. Furthermore, inherited components must be used as intended in the superclass.

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SAP

If you misunderstand the statement “is a (specific)”, you run the risk of identifying wrong places in which to use inheritance. Sometimes the need for another attribute for a class is incorrectly answered with a specialization. For example:

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Figure 111: Examples: Misuse of Inheritance


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In some cases, specialization relationships are identified that do not allow for the semantics to be preserved. For example:

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For the same reasons, simple inheritance of the source text – that is, using inheritance only because some required functions were found in a (super)class – is also impossible.

SAP

The class Square inherits from the class Rectangle. If you try to define methods for the rectangle that change the width and height separately, these methods would not make sense when applied to the square. Even if the methods had been redefined to change the lengths of the sides in uniform, the semantics would be different.

Use

Partner

Note: Such attributes are often also defined as reference variables to a superclass of role classes. There is one description class for each role. To change the role of an instance, you then exchange the references to the corresponding role description instances. Specialist literature also refers to this as a “role design pattern”.

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A superclass Car contains the subclasses Red Car, Blue Car, and so on. The statement “A red car is a specific car” is only correct at first glance. However, there are no cars without a color. At best, there are some cars that have not been painted. Therefore, every car needs the attribute Color, assuming that it is relevant to the application. Therefore, the attribute should already have been defined in the superclass, or there is no longer an authorization for subclasses of this type. There would also be contradictions with reality when you try to implement a method for painting the cars.

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Exercise 11: Class Hierarchies Exercise Objectives

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After completing this exercise, you will be able to: • Define subclasses • Redefine superclass methods in subclasses • Use visibility sections effectively

Business Example

Task 1: In the class LCL_AIRPLANE, define the local subclass LCL_PASSENGER_PLANE for passenger planes. Complete your program ZBC401_##_MAIN program or copy the program SAPBC401_AIRS_MAIN_E (where ## is your two-digit group number).

The class must have a private instance attribute MAX_SEATS with the same type as the table field SFLIGHT-SEATSMAX.

3.

Define and implement an instance constructor that assigns values to all instance attributes in the class.

4.

Redefine DISPLAY_ATTRIBUTES so that all instance attributes are displayed using the WRITE statement.

Task 2: In the class LCL_AIRPLANE, define the local subclass LCL_CARGO_PLANE for cargo planes. 1.

The class must have a private instance attribute MAX_CARGO with the same type as the table field SCPLANE-CARGOMAX.

2.

Define and implement an instance constructor that assigns values to all instance attributes in the class. Continued on next page

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2.

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If applicable, enter the source code for your new class in the include program.

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1.

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Your airplane management program is to be refined further. Put specific airplanes in relation to their general airplane class.


3.

BC401

Redefine DISPLAY_ATTRIBUTES so that all instance attributes are displayed using the WRITE statement.

Task 3:

Partner

In the main program, define a suitably typed reference variable for each of your new classes.

2.

Call the static method DISPLAY_N_O_AIRPLANES (before instantiating any objects).

3.

Use the two references to create an instance of each of the subclasses LCL_PASSENGER_PLANE and LCL_CARGO_PLANE. Decide for yourself how to fill the attributes.

4.

Call the DISPLAY_ATTRIBUTES method for both instances.

5.

Call the static method DISPLAY_ATTRIBUTES a second time.

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1.

Task 4:

SAP

2.

Could the method GET_TECHNICAL_ATTRIBUTES be called directly from the redefined method DISPLAY_ATTRIBUTES of the subclasses?

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Observe the program flow in the ABAP Debugger, paying special attention to the call of the DISPLAY_ATTRIBUTES method.

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1.

SAP

Analyze your program.

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Create instances of your new classes and display their attributes.

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Solution 11: Class Hierarchies Task 1: In the class LCL_AIRPLANE, define the local subclass LCL_PASSENGER_PLANE for passenger planes. Complete your program ZBC401_##_MAIN program or copy the program SAPBC401_AIRS_MAIN_E (where ## is your two-digit group number). If applicable, enter the source code for your new class in the include program.

b) 2.

The class must have a private instance attribute MAX_SEATS with the same type as the table field SFLIGHT-SEATSMAX. a)

SAP

Define and implement an instance constructor that assigns values to all instance attributes in the class. a)


Redefine DISPLAY_ATTRIBUTES so that all instance attributes are displayed using the WRITE statement. a)


In the class LCL_AIRPLANE, define the local subclass LCL_CARGO_PLANE for cargo planes. 1.

The class must have a private instance attribute MAX_CARGO with the same type as the table field SCPLANE-CARGOMAX. a)

2.


Define and implement an instance constructor that assigns values to all instance attributes in the class. a)



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Task 2:

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4.


SAP

3.

Carry out this step in the usual manner. Additional information is available in the SAP Library. Model solution: SAPBC401_INHS_MAIN_A

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a)

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1.


3.

BC401

Redefine DISPLAY_ATTRIBUTES so that all instance attributes are displayed using the WRITE statement. a)


Task 3: Create instances of your new classes and display their attributes. In the main program, define a suitably typed reference variable for each of your new classes. a)

Call the static method DISPLAY_N_O_AIRPLANES (before instantiating any objects). a)

3.

Use the two references to create an instance of each of the subclasses LCL_PASSENGER_PLANE and LCL_CARGO_PLANE. Decide for yourself how to fill the attributes. a)

SAP

Call the DISPLAY_ATTRIBUTES method for both instances. a)

5.


Call the static method DISPLAY_ATTRIBUTES a second time. See the source code extract from the model solution

Task 4: 1.

Observe the program flow in the ABAP Debugger, paying special attention to the call of the DISPLAY_ATTRIBUTES method. a)

2.


Could the method GET_TECHNICAL_ATTRIBUTES be called directly from the redefined method DISPLAY_ATTRIBUTES of the subclasses? Answer: No, because the component of the superclass is private


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Analyze your program.

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a)

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4.


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2.


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1.

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SAPBC401_INHS_MAIN_A REPORT

sapbc401_inhs_main_a.

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TYPE-POOLS icon.

INCLUDE sapbc401_inhs_a.


Partner

r_cargo TYPE REF TO lcl_cargo_plane, r_passenger TYPE REF TO lcl_passenger_plane, plane_list TYPE TABLE OF REF TO lcl_airplane.

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START-OF-SELECTION.

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SAP

*##############################


CREATE OBJECT r_passenger EXPORTING

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im_name = ’LH BERLIN’ im_planetype = ’747-400’ im_seats = 345.

Internal

CREATE OBJECT r_cargo EXPORTING im_name = ’US Hercules’ im_planetype = ’747-500’ im_cargo = 533.

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r_cargo->display_attributes( ).

r_passenger->display_attributes( ).



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SAPBC401_INHS_A *&---------------------------------------------------------------------* *&

Include

SAPBC401_INHS_A

*

*&---------------------------------------------------------------------* *------------------------------------------------------------------* *


*

*------------------------------------------------------------------*

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CLASS lcl_airplane DEFINITION. PUBLIC SECTION. "-------------------------------CONSTANTS: pos_1 TYPE i VALUE 30.

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TYPE string


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SAP

PRIVATE SECTION. "---------------------------------METHODS: get_technical_attributes IMPORTING im_type

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ex_tankcap DATA: name

TYPE saplane-planetype TYPE s_plan_wei

Partner

EXPORTING ex_weight

TYPE s_capacity.

TYPE string,

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ENDCLASS.


*------------------------------------------------------------------* *


*

*------------------------------------------------------------------* CLASS lcl_airplane IMPLEMENTATION. METHOD constructor. name

= im_name.


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planetype

= im_planetype.


"constructor

METHOD display_attributes. DATA: weight TYPE saplane-weight, cap TYPE saplane-tankcap. WRITE: / icon_ws_plane AS ICON,

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/ ’Name des Flugzeugs’(001), AT pos_1 name, / ’Type of airplane: ’(002), AT pos_1 planetype. get_technical_attributes( EXPORTING im_type = planetype IMPORTING ex_weight = weight ex_tankcap = cap ).

Partner

WRITE: / ’Gewicht:’(003), weight, ’Tankkap:’(004), cap. ENDMETHOD.

"display_attributes

Use

METHOD display_n_o_airplanes. WRITE: /, / ’Number of airplanes: ’(ca1), AT pos_1 n_o_airplanes LEFT-JUSTIFIED, /.

SAP


SAP

ENDMETHOD.


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WHERE planetype = im_type. IF sy-subrc 0. ex_weight = 100000. ex_tankcap = 10000.


"get_technical_attributes

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ENDIF.


*---------------------------------------------------------------------* *

CLASS lcl_cargo_plane DEFINITION

*---------------------------------------------------------------------* * *---------------------------------------------------------------------* CLASS lcl_cargo_plane DEFINITION INHERITING FROM lcl_airplane.


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PUBLIC SECTION. "---------------------METHODS: constructor IMPORTING im_name TYPE string im_planetype TYPE saplane-planetype im_cargo TYPE scplane-cargomax. METHODS: display_attributes REDEFINITION.

"---------------------DATA: max_cargo TYPE scplane-cargomax.

"lcl_cargo_plane DEFINITION

*---------------------------------------------------------------------* *

CLASS lcl_cargo_plane IMPLEMENTATION

*---------------------------------------------------------------------* * *---------------------------------------------------------------------*

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CLASS lcl_cargo_plane IMPLEMENTATION.

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ENDCLASS.

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PRIVATE SECTION.

METHOD constructor. CALL METHOD super->constructor( im_name = im_name im_planetype = im_planetype ). max_cargo = im_cargo.

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"constructor

ENDMETHOD.

METHOD display_attributes.

Internal

super->display_attributes( ). WRITE: / ’Max Cargo = ’, max_cargo. ULINE.

ENDCLASS.

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ENDMETHOD.

"display_attributes

"lcl_cargo_plane IMPLEMENTATION

*---------------------------------------------------------------------* *

CLASS lcl_passenger_plane DEFINITION

*---------------------------------------------------------------------* * *---------------------------------------------------------------------* CLASS lcl_passenger_plane DEFINITION INHERITING FROM lcl_airplane..


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PUBLIC SECTION. METHODS: constructor IMPORTING im_name TYPE string im_planetype TYPE saplane-planetype im_seats TYPE sflight-seatsmax. METHODS: display_attributes REDEFINITION.

PRIVATE SECTION.

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DATA: max_seats TYPE sflight-seatsmax. "lcl_passenger_plane DEFINITION

ENDCLASS.

*---------------------------------------------------------------------* *

CLASS lcl_passenger_plane IMPLEMENTATION

Partner

*---------------------------------------------------------------------* * *---------------------------------------------------------------------*

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CLASS lcl_passenger_plane IMPLEMENTATION.

METHOD constructor. CALL METHOD super->constructor( EXPORTING im_name

= im_name

SAP

SAP

im_planetype = im_planetype ). max_seats = im_seats. "constructor

ENDMETHOD.


Partner

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super->display_attributes( ). WRITE: / ’Max Seats = ’, max_seats. ULINE.

Internal

ENDMETHOD.

ENDCLASS.

"display_attributes "lcl_passenger_plane IMPLEMENTATION

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Exercise 12: Polymorphism Exercise Objectives After completing this exercise, you will be able to: • Program narrowing cast assignments • Use inheritance relationships for polymorphic method calls

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Task 1: 1.


2.

In your main program, define an internal table for buffering airplane references. The row type of the internal table should be REF TO LCL_AIRPLANE.

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Partner

Task 2: Insert the references to your passenger and cargo airplanes into the internal table.

2.

Program a loop through the contents of the internal table. Call the DISPLAY_ATTRIBUTES method every time the loop runs.

Only

Internal

Display the attributes of all airplane types that were created so far. 1.

Task 3: Analyze your program. 1.

Follow the program flow in the ABAP Debugger, paying special attention to the call of the DISPLAY_ATTRIBUTES method.


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SAP

Buffer the airplane references in a suitable type of internal table.

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Your airplane management program should display the attributes of the airplane objects generically, that is, it should be open to future extensions with additional airplane classes.

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What would happen if the DISPLAY_ATTRIBUTES method had not been redefined in the subclasses?

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Solution 12: Polymorphism Task 1: Buffer the airplane references in a suitable type of internal table. 1.


b)

In your main program, define an internal table for buffering airplane references. The row type of the internal table should be REF TO LCL_AIRPLANE. a)


Use

Partner

2.

Carry out this step in the usual manner. Additional information is available in the SAP Library. Model solution: SAPBC401_CASS_MAIN_A

Task 2: Display the attributes of all airplane types that were created so far.

SAP

Insert the references to your passenger and cargo airplanes into the internal table. a)

Use


Program a loop through the contents of the internal table. Call the DISPLAY_ATTRIBUTES method every time the loop runs. a)

Partner

2.

SAP

1.


Analyze your program. Follow the program flow in the ABAP Debugger, paying special attention to the call of the DISPLAY_ATTRIBUTES method. a) 2.


What would happen if the DISPLAY_ATTRIBUTES method had not been redefined in the subclasses? Answer: The implementation from the superclass would be executed. Your program would not contain polymorphism. Continued on next page

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Task 3: 1.

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SAPBC401_CASS_MAIN_A REPORT

sapbc401_cass_main_a.

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TYPE-POOLS icon.

INCLUDE sapbc401_inhs_a. DATA: r_plane TYPE REF TO lcl_airplane, r_cargo TYPE REF TO lcl_cargo_plane,

Partner

r_passenger TYPE REF TO lcl_passenger_plane, plane_list TYPE TABLE OF REF TO lcl_airplane.

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SAP

lcl_airplane=>display_n_o_airplanes( ). CREATE OBJECT r_passenger EXPORTING im_name = ’LH BERLIN’

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im_planetype = ’747-400’ im_seats = 345. APPEND r_passenger TO plane_list.

Internal

CREATE OBJECT r_cargo EXPORTING im_name = ’US HErcules’ im_planetype = ’747-500’ im_cargo = 533.

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APPEND r_cargo TO plane_list.

LOOP AT plane_list INTO r_plane. r_plane->display_attributes( ). ENDLOOP.


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Exercise 13: Aggregation and Generic Calls Exercise Objectives

Business Example

Task 1:

Use Internal

2.

Extend the signature and implementation of method ADD_AIRPLANE so that the airplane references can be added to the previously defined list AIRPLANE_LIST.

3.

Extend the implementation of method DISPLAY_AIRPLANES so that the attributes of all airplanes of the airline can be added to the list. Each time an airplane is added, its DISPLAY_ATTRIBUTES method should be called.

4.

Extend the implementation of the DISPLAY_ATTRIBUTES method so that all of attributes of the airline can be displayed and, consequently, the contents of the airplane list can also be displayed.

Task 2: In the main program, create an airline instance. Transfer some airplane references to it and display the attributes. 1.

Remove all the statements from the main program that define the global internal table for airplane references and their insertions. Continued on next page

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From the include program SAPBC401_CAST_B, copy the portions of the source text for the local class LCL_CARRIER into your include program ZBC401_##_AIRPLANE so that you can add to them there. (Where ## is your two-digit group number).

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1.

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SAP

Define a local class for airlines.

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Partner

Now, the management of airplane instances should no longer take place in the main program. Instead, it should be encapsulated in a new class for airlines.

Internal

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After completing this exercise, you will be able to: • Implement aggregation relationships between classes • Program narrowing cast assignments • Use inheritance relationships for polymorphic method calls

BC401

In the main program, define a suitably typed reference variable for your new airline class.

3.

Using the reference, generate an instance of your class LCL_CARRIER. Decide for yourself how to fill the attributes.

4.

Call the ADD_AIRPLANE method to transfer the airplane instances that have been created so far to the airline. You may also create and transfer additional airplanes.

5.

Display the attributes of the airline by calling its DISPLAY_ATTRIBUTES method.

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Solution 13: Aggregation and Generic Calls Task 1: Define a local class for airlines. From the include program SAPBC401_CAST_B, copy the portions of the source text for the local class LCL_CARRIER into your include program ZBC401_##_AIRPLANE so that you can add to them there. (Where ## is your two-digit group number). a) b)

Extend the signature and implementation of method ADD_AIRPLANE so that the airplane references can be added to the previously defined list AIRPLANE_LIST. a)

Extend the implementation of method DISPLAY_AIRPLANES so that the attributes of all airplanes of the airline can be added to the list. Each time an airplane is added, its DISPLAY_ATTRIBUTES method should be called. a)

Use

Extend the implementation of the DISPLAY_ATTRIBUTES method so that all of attributes of the airline can be displayed and, consequently, the contents of the airplane list can also be displayed. See the source code extract from the model solution

Task 2: In the main program, create an airline instance. Transfer some airplane references to it and display the attributes. 1.

Remove all the statements from the main program that define the global internal table for airplane references and their insertions. a)

2.


In the main program, define a suitably typed reference variable for your new airline class. a)


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a)

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4.


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SAP

3.


Use

Partner

2.

Carry out this step in the usual manner. Additional information is available in the SAP Library. Model solution: SAPBC401_CASS_MAIN_B

Internal

Only

1.


3.

Using the reference, generate an instance of your class LCL_CARRIER. Decide for yourself how to fill the attributes. a)

4.


Display the attributes of the airline by calling its DISPLAY_ATTRIBUTES method. a)


Partner


Use

SAPBC401_CASS_MAIN_B sapbc401_cass_main_b.

SAP

SAP

REPORT

TYPE-POOLS icon.

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INCLUDE sapbc401_cass_b.

DATA: r_plane TYPE REF TO lcl_airplane, r_cargo TYPE REF TO lcl_cargo_plane, r_passenger TYPE REF TO lcl_passenger_plane,

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r_carrier TYPE REF TO lcl_carrier.

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START-OF-SELECTION. *############################## ***** Create Carrier ******************************************** CREATE OBJECT r_carrier EXPORTING im_name = ’Smile&Fly Travel’.

***** Passenger Plane ******************************************** CREATE OBJECT r_passenger EXPORTING im_name = ’LH BERLIN’ im_planetype = ’747-400’


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Call the ADD_AIRPLANE method to transfer the airplane instances that have been created so far to the airline. You may also create and transfer additional airplanes. a)

5.

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im_seats = 345. ***** cargo Plane ************************************************ CREATE OBJECT r_cargo EXPORTING im_name = ’US HErcules’ im_planetype = ’747-500’ im_cargo = 533.

***** insert planes into itab if client ***************************

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r_carrier->add_airplane( r_passenger ).

Partner

r_carrier->add_airplane( r_cargo ).

***** show all airplanes inside carrier *************************** r_carrier->display_attributes( ).

Use

SAPBC401_CASS_B *&

Include

SAPBC401_CASS_B

SAP

SAP

*&---------------------------------------------------------------------* *

*&---------------------------------------------------------------------*

*------------------------------------------------------------------*

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*

*

*------------------------------------------------------------------* ... *---------------------------------------------------------------------*

Internal

*

CLASS lcl_carrier DEFINITION

*---------------------------------------------------------------------* *

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*---------------------------------------------------------------------* CLASS lcl_carrier DEFINITION. PUBLIC SECTION. "---------------------------------------METHODS: constructor IMPORTING im_name TYPE string, get_name RETURNING value(ex_name) TYPE string, add_airplane IMPORTING im_plane TYPE REF TO lcl_airplane, display_airplanes,


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display_attributes. PRIVATE SECTION. "----------------------------------DATA: name

TYPE string,

airplane_list TYPE TABLE OF REF TO lcl_airplane. ENDCLASS.

"lcl_carrier DEFINITION

*---------------------------------------------------------------------* CLASS lcl_carrier IMPLEMENTATION

*---------------------------------------------------------------------* CLASS lcl_carrier IMPLEMENTATION. METHOD add_airplane.

Partner

APPEND im_plane TO airplane_list. ENDMETHOD.

"add_airplane

Use

METHOD display_attributes. WRITE: icon_flight AS ICON, name . ULINE. ULINE. display_airplanes( ). "display_attributes

SAP

SAP

ENDMETHOD.

Internal

Only

*

METHOD display_airplanes. DATA: r_plane TYPE REF TO lcl_airplane. LOOP AT airplane_list INTO r_plane.

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Use

r_plane->display_attributes( ). ENDLOOP. ENDMETHOD.

"display_airplanes

Internal

METHOD constructor. name = im_name. ENDMETHOD.

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METHOD get_name. ex_name = name. ENDMETHOD.

ENDCLASS.

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"get_name

"lcl_carrier IMPLEMENTATION


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Lesson Summary

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Related Information

Use

Partner


Internal

You should now be able to: • Define inheritance relationships between classes • Redefine methods • Create narrowing cast assignments • Create widening cast assignments • Explain the concept of polymorphism with reference to interfaces • Use cast assignments with inheritance to make generic calls

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Lesson: Interfaces and Casting Lesson Overview The only real difference between interfaces and inheritance is the role they play. The programming advantages are thus the same as for inheritance. Therefore, the former will be the first focus of this lesson.

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Internal


Partner

Define and implement interfaces Implement interface methods Use interface references to make narrowing cast assignments Use interface references to make widening cast assignments Explain the term polymorphism with reference to interfaces Use cast assignments with interfaces to make generic calls

Use

• • • • • •

SAP

You want to implement client/server relationships in combination with generic access from your model in ABAP Objects.

Use

Interfaces differ from regular inheritance in their area of use. In terms of programming, there are hardly any differences, however.

Internal

In ABAP Objects, interfaces primarily serve to define uniform interfaces (protocols) for services. Various classes can thus offer – that is, implement – these services in different ways, but keep the same semantics. Interfaces therefore contain no implementations. In ABAP Objects, the same components can generally be defined in interfaces and in classes. To recognize the semantic differences from regular inheritance, you can concentrate on the following, typical use cases:

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From a technical point of view, interfaces are simply superclasses that cannot be instantiated, do not have an implementation part, and only have public components. However, we will see that you can simulate multiple inheritance using interfaces.

Partner

Areas of Use for Interfaces

SAP

Business Example

BC401

Lesson: Interfaces and Casting

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Internal

Figure 112: Central Definition of Shared Components

SAP

SAP

Use

For example, you want to allow for the option of having multiple classes implementing a service in different ways, but using the same method names and with a uniform signature. With regular inheritance, you would define such a method in the shared superclass. However, if you cannot model a superclass suitably for inheritance, you need to define an interface and then define this method there. Therefore, you can compare this case with a generalization relationship with a superclass.

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Figure 113: The Client Defines the Protocol

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Compared to regular inheritance, distribution of roles is sometimes different: The user generally defines the interfaces. In these, the user describes (both technically and semantically) the services that he/she wants the providers to offer. Each class can now decide for itself whether it serves the interface, that is, actually offers the services defined there. Therefore, this case is similar to a specialization relationship with a subclass.

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Internal

As with regular inheritance, access to these services is then usually generic, that is, using a reference that is typed on the interface. As with regular inheritance, you can thus perform polymorphism with interfaces.

Internal

The similarity with representing a generalization/specialization relationship is justified, as we have just described.

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In UML, interfaces are represented in the same way as classes. However, in addition to their name, they bear the stereotype «interface.» The use of an interface is represented by a dotted line with a two-sided arrow from the user to the interface; the stereotype «uses» is optional. The fact that a class implements an interface is represented by a dotted arrow from the class to the interface.

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SAP

Figure 114: Interfaces in UML Notation

BC401


Realization of Generalization/Specialization Relationships Using Interfaces In ABAP Objects, the same components can be defined in an interface as in classes. However, interfaces do not know the visibility levels of components, that is, all components of an interface are public. Note: Note the areas of use for interfaces as the uniform interface for offering services.

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Internal

•

• •

The interface name is listed in the definition part of the class with the INTERFACES statement. This must be in the PUBLIC SECTION, that is, interfaces can only be implemented publicly. The interface methods must be implemented in the implementation part of the class. The components defined in the interface can be addressed in the implementation part of the class.

Interface components are distinguished from the other components in the implementing class by prefixing the interface name followed by a tilde ~ (the interface resolution operator): interface_name~component_name.

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Classes implement interfaces as follows:

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SAP

SAP

Figure 115: Defining and Implementing an Interface


BC401

To simplify accessing interface components you can work with alias names. These can only appear in the definition part of a class or in the interface definition. Their use is subject to the visibility restriction of the defining class. Example of an alias in the interface: ALIASES a_1 FOR lif_1~method_1.

Only

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Partner

Internal

The interface method lif_1~method_1 can then be addressed with the shorter form ref->a_1 .

Internal

Alternatively, you can use the alias names defined in the implementing class for the interface components. Even if shared components of the implementing classes subsequently are transferred to the interface, access to

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Interface components can only be accessed by using an object reference, whose class implements the interface. Syntactically, this takes place with the interface resolution operator ~ , just as with access to the interface components in the implementation part of the class.

Partner

Use

SAP

SAP

Figure 116: Addressing Interface Components Using Object References

BC401


these components does not need to be adapted. However, the source text would then be less self-explanatory because you could conclude from the syntax that the components were defined in the class.

Polymorphism with Interfaces

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Partner

Internal

Because interfaces cannot be instantiated, an interface reference can only refer to instances of classes that have implemented the interface. Therefore, if you want to perform polymorphism with interfaces, you must use narrowing cast to copy a reference to the reference variable that was typed with the interface – as with regular inheritance.

Internal

A user can thus address the instance of the implementing class using the interface. The prefixing of the interface name and the interface resolution operator is thus omitted. However, the user is restricted to using the components from the interface.

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If the class has implemented the interface, it is certain that all components that can be accessed syntactically after the cast assignment are actually available in the instance. The interface always contains at least the same components as the implementing class.

Partner

Use

SAP

SAP

Figure 117: Narrowing Cast with Interface References


BC401

In the example shown here, the methods DISPLAY_PARTNER and CHECK_AVAILABILITY of the interface LIF_PARTNER can only be accessed after assigning the reference variable R_PARTNER. It is not possible to access the specific components of the instance from class LCL_RENTAL (GET_NAME in the above example) using the reference variable R_PARTNER.

Only

Use

Partner

Internal

The view is thus restricted as a rule (usually observed). That is why we describe this type of assignment of reference variables as narrowing cast. There is a switch from a view of several components to a view of a few components. The term upcast is also common.

Internal

In the example shown here, a travel agency (LCL_TRAVEL_AGENCY) needs to manage all the various kinds of business partner in one list. The row type of the internal table must therefore be typed as the reference to the interface LIF_PARTNER. The travel agency only wants to request the services in order to display their attributes and to check availability. The relevant methods DISPLAY_PARTNER and CHECK_AVAILABILITY are defined in the interface LIF_PARTNER and implemented in all business partner classes.

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A typical area of use for narrowing cast assignments is preparation for generic access: A user, who is not at all interested in the finer points of the instances of the classes that implement the interface but who simply wants to address the components defined in the interface, could use an interface reference for this access.

Partner

Use

SAP

SAP

Figure 118: Row Type of the Internal Table in the Application Example

BC401


Objects of different classes (LCL_HOTEL, LCL_RENTAL, and LCL_CARRIER in the above example) can be kept in an internal table, typed with interface references (LIF_PARTNER in the above example). The components defined in the interface can then be accessed uniformly. For this example, method ADD_PARTNER is therefore needed. This copies the references to all the kinds of business partner in this internal table. It is import parameter is already typed as the reference to the interface.

Use

Partner

Only

Internal

The dynamic type and not the static type of the reference variable is used to search for the implementation of a method. In the above example, r_partner->display_partner( ) therefore uses the class of the instance that r_partner actually refers to to search for the implementation of display_partner . The static type for r_partner , which is always REF TO lif_partner

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Internal

Polymorphism can also be performed for interfaces: Interface references can be used to call methods, whereby different implementations can be executed depending on the object of the reference.

Partner

Use

SAP

SAP

Figure 119: Polymorphism – Generic Access Using the Interface Reference


BC401

, is not used. The implementation that is now executed when DISPLAY_PARTNER is called therefore depends on the object to which the interface reference R_PARTNER currently refers. When objects from different classes react differently to the same method calls, this is known as polymorphism.

Only

Polymorphism can be used to write programs that are highly generic, that is, they do not need to be changed significantly if use cases are added.

Partner

Use

In the example given here, it would therefore be very easy to realize a boat rental addition: The relevant class – for example, with the name LCL_SHIPPING – would simply have to implement the interface LIF_PARTNER and thus the method DISPLAY_PARTNER defined there. Business partner management could then include shipping companies without problem and also request them to display their attributes.

Internal

The option of performing polymorphism is one of the main strengths of interfaces: A client can handle different classes uniformly, irrespective of their implementation. The runtime system searches for the right implementation of a method on behalf of the client.

SAP

SAP Only

Internal

Use

Partner

Figure 120: Widening Cast Assignment and Exception Handling in the Application Example

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Partner

Use

SAP

That is why with this kind of cast, the runtime system checks, before the assignment, whether the current content of the source variable corresponds to the type requirements of the target variable. Otherwise, an exception that can be handled is triggered, and the original value of the target variable remains the same. This exception of error class CX_SY_MOVE_CAST_ERROR can be identified using TRY-ENDTRY and the CATCH statement.

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Therefore, what happens if there is no airline reference in the interface reference R_PARTNER at runtime but the widening cast assignment operator is used to copy the reference to the then invalid reference R_CARRIER? In contrast to the narrowing cast assignment, it is possible that the static type of the target variable (R_CARRIER) is neither more general than nor the same as the dynamic type of the source variable (R_PARTNER), namely when R_PARTNER contains hotel or car rental references.

Partner

A typical area of use for widening cast assignments is when specific components of instances need to be addressed whose references are kept in variables that are typed on the interface. A user who is interested in the finer points of instances of implementing classes cannot use the interface reference for this access because this only allows access to the interface components. In the example shown here, a travel agency (LCL_TRAVEL_AGENCY) needs to book a flight but keeps all the various business partner references in an internal table that was typed on the interface LIF_PARTNER.

SAP

Use

The view is thus widened (at least unchanged). That is why we describe this type of assignment of reference variables as widening cast. There is a switch from a view of a few components to a view of more components. The term downcast is also common.

Internal

Interface reference variables can contain references to instances of the implementing class at runtime. After assigning this type of reference (back) to a reference to the implementing class, clients are no longer limited to interface components: In the example given here, all components of the LCL_CARRIER instance can be accessed (again) after the assignment using reference R_CARRIER.

Internal

Only

If you want to assign an interface reference to a class reference where the class has implemented the interface, you must use the widening cast assignment operator MOVE ... ?TO ... or its short form ?= . Otherwise, the system would return a message stating that it is not certain that all components that can be accessed syntactically after the cast assignment are actually available in the instance. As a rule, the implementing class contains more components than the interface.


BC401

Another way of preventing this runtime error would be to use runtime type identification (RTTI) classes. They can be used to determine the dynamic type at runtime and to set a condition for the cast.

Only

Interface Hierarchies

Use

Partner

We have already seen several times that an interface implementation strongly resembles regular inheritance. We therefore need to ask what the interface counterpart of hierarchical inheritance looks like. We want to explain interface hierarchies using an application example:

Internal

Assignments between interface reference variables, whose typing interfaces are not related to each other, cannot be checked statically either and must therefore be performed using widening cast. With such an assignment, the system checks at runtime whether the class of the instance to which the source reference refers also supports the interface with which the target reference is typed.

SAP

SAP

In this example, we need to know whether it would be useful to define a further service “room reservation” in the interface LIF_PARTNER. In this case, the classes LCL_CARRIER and LCL_RENTAL would have to implement the appropriate method because they have integrated the interface LIF_PARTNER. However, implementation of a room reservation – keeping the same semantics – is not conceivable for airlines or car rental companies.

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Internal

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Partner

Figure 121: Interface Hierarchy in the Application Example

BC401


However, because there are several other business partner types for which an implementation would be useful (for example, motels and hotels), the method needs to be centrally defined and not individually for motels and hotels. On the other hand, the option of easily extending the model with other accommodation provider types (for example, guesthouse) must be retained.

Use

The including interface is known as a compound interface. An included interface represents a component of another interface and is therefore known as a component interface. An elementary interface does not itself contain other interfaces. The UML notation corresponds to the implementation of an elementary interface by a class.

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Internal

You can thus regard the including interface as a specialization of the included interface. It represents an extension of the included interface.

Partner

In ABAP Objects, interfaces – like regular superclasses – can include other interfaces. As with regular inheritance, the result is interface hierarchies of any “depth.”

SAP

SAP

Use

Partner

Only

Internal

Figure 122: Compound Interface in UML Notation


BC401

SAP Use

Only

Internal

All implementations of methods from all higher-level interfaces must take place in the first implementing class. Alias names are suitable for short-form syntax when accessing components from different interfaces. At the same time, you get a central documentary view of all components with the definition of these alias names in the implementing class.

Partner

They are therefore not prefixed with the name of the compound interface.

SAP

As with regular inheritance, the implementing class only needs to list the compound interface in order to integrate all components. Nevertheless, the components of the component interfaces keep their original names, that is, component_interface_name~component_name.

Use

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Only

Internal

Figure 123: Definition and Implementation of Compound Interfaces – Syntax

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Figure 124: Addressing Components in Compound Interfaces – Syntax

The same possibilities apply for access its components from a compound interface and for cast assignments.

Use

Partner

Only

BC401

SAP

SAP Only

Internal

Use

Partner

Figure 125: Using Interfaces

Interfaces are used to describe protocols for using components without connecting a kind of implementation. An “intermediate” layer is introduced between the client and the server to protect the client from the explicit server, thereby making the client independent.

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Interfaces enable different classes to be handled uniformly, providing they implemented the interfaces. As with inheritance, you can also perform polymorphism using interface reference variables. As with regular inheritance, the definition of an interface means an abstraction of the implementing classes to a specific partial aspect. Multiple inheritance can be simulated using interfaces: If several interfaces are included, all components are available to all of these interfaces. All methods must be implemented.

Use

Partner

Only

Internal

SAP

SAP Only

Internal

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Partner

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Exercise 14: Interface Implementation Exercise Objectives After completing this exercise, you will be able to: • Define interfaces • Implement interfaces

Only

Task 1:

From the include program SAPBC401_VEHT_F, copy the portions of the source text for the local classes LCL_VEHICLE, LCL_TRUCK, LCL_BUS, and LCL_RENTAL into a new include program ZBC401_##_VEHICLE to extend them there if necessary. (Where ## is your two-digit group number). Include this new include program in your main program.

3.

From the program SAPBC401_VEHT_MAIN_A, copy the portions of the source text for the data types TY_FUEL and TY_CARGO for the definitions of the reference variables, for the generation of the instances, and for the method calls in your main program to extend them there if necessary.

4.

To test your work so far, call the method DISPLAY_ATTRIBUTES for the car rental company. The list should now display all airplanes of your airline and all vehicles of your car rental company.

Internal

Use

2.


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Only

Complete your program ZBC401_##_MAIN program or copy the program SAPBC401_CASS_MAIN_B (where ## is your two-digit group number).

Partner

1.

SAP

SAP

Define a class for car rental companies and a class hierarchy for general vehicles, buses, and trucks. Generate a car rental company and add a few vehicle instances. Add the attributes of the car rental company to the list.

Use

Partner

You now need to add a vehicle management procedure to your airplane management program. The airlines and car rental companies then need to be abstracted to business partners; that is, they need to offer general services using an abstract interface.

Internal

Business Example


BC401

Task 2: Define and implement an interface for offering general services from business partners. 1.

Remove the calls of method DISPLAY_ATTRIBUTES from your main program again.

2.

If necessary, add an interface LIF_PARTNERS to your UML diagram. This needs to define a method DISPLAY_PARTNER. Draw the relationships to the classes LCL_RENTAL and LCL_CARRIER.

3.

Define the local interface LIF_PARTNERS and the method DISPLAY_PARTNER.

Use

Partner

Caution: You will therefore not receive any output on the list until the next exercise.

SAP Use

Only

Internal

Partner

Implement the interface in the classes LCL_CARRIER and LCL_RENTAL. You need to realize the display of a business partner’s attributes in such a way that they call their own methods DISPLAY_ATTRIBUTES.

SAP

Hint: Include the portions of the source text needed for this in your main program in an appropriate order with the remaining class definitions. 4.

Internal

Only

Note: In the following, you need to store the relevant list outputs as a general service.

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Solution 14: Interface Implementation Task 1: Define a class for car rental companies and a class hierarchy for general vehicles, buses, and trucks. Generate a car rental company and add a few vehicle instances. Add the attributes of the car rental company to the list. Complete your program ZBC401_##_MAIN program or copy the program SAPBC401_CASS_MAIN_B (where ## is your two-digit group number). a)

2.

From the include program SAPBC401_VEHT_F, copy the portions of the source text for the local classes LCL_VEHICLE, LCL_TRUCK, LCL_BUS, and LCL_RENTAL into a new include program ZBC401_##_VEHICLE to extend them there if necessary. (Where ## is your two-digit group number). Include this new include program in your main program.

SAP

From the program SAPBC401_VEHT_MAIN_A, copy the portions of the source text for the data types TY_FUEL and TY_CARGO for the definitions of the reference variables, for the generation of the instances, and for the method calls in your main program to extend them there if necessary.

4.


To test your work so far, call the method DISPLAY_ATTRIBUTES for the car rental company. The list should now display all airplanes of your airline and all vehicles of your car rental company. a)



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a)

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3.


SAP

a)

Use

Partner

b)

Carry out this step in the usual manner. Additional information is available in the SAP Library. Model solution: SAPBC401_INTS_MAIN_A

Internal

Only

1.


BC401

Task 2: Define and implement an interface for offering general services from business partners. 1.

Remove the calls of method DISPLAY_ATTRIBUTES from your main program again.

Caution: You will therefore not receive any output on the list until the next exercise.

2.

If necessary, add an interface LIF_PARTNERS to your UML diagram. This needs to define a method DISPLAY_PARTNER. Draw the relationships to the classes LCL_RENTAL and LCL_CARRIER. Speak to your instructor if you have any questions.

SAP

SAP

a) 3.


Define the local interface LIF_PARTNERS and the method DISPLAY_PARTNER.

Use

Implement the interface in the classes LCL_CARRIER and LCL_RENTAL. You need to realize the display of a business partner’s attributes in such a way that they call their own methods DISPLAY_ATTRIBUTES. a)




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4.


Partner

Hint: Include the portions of the source text needed for this in your main program in an appropriate order with the remaining class definitions. a)

Use

Partner

a)

Internal

Only

Note: In the following, you need to store the relevant list outputs as a general service.

BC401


SAPBC401_INTS_MAIN_A REPORT

sapbc401_ints_main_a.

TYPES ty_fuel TYPE p DECIMALS 2. TYPES ty_cargo TYPE p DECIMALS 2. TYPE-POOLS icon.

INCLUDE sapbc401_vehd_f.

Only

Internal

INCLUDE sapbc401_ints_a.

DATA: r_plane TYPE REF TO lcl_airplane, r_cargo TYPE REF TO lcl_cargo_plane, r_passenger TYPE REF TO lcl_passenger_plane,

Partner

r_carrier TYPE REF TO lcl_carrier, r_rental TYPE REF TO lcl_rental, r_truck TYPE REF TO lcl_truck,

Use

r_bus TYPE REF TO lcl_bus.

START-OF-SELECTION.

SAP

SAP

*############################## ***** Create CARRIER ******************************************** CREATE OBJECT r_carrier EXPORTING im_name = ’Smile&Fly Travel’.

Use

Partner

***** Passenger Plane ******************************************** CREATE OBJECT r_passenger EXPORTING im_name = ’LH BERLIN’ im_planetype = ’747-400’

Internal

im_seats = 345. ***** cargo Plane ************************************************ CREATE OBJECT r_cargo EXPORTING

Only

im_name = ’US HErcules’ im_planetype = ’747-500’ im_cargo = 533. ***** insert planes into itab if client *************************** r_carrier->add_airplane( r_passenger ). r_carrier->add_airplane( r_cargo ). ***** show all airplanes inside carrier *************************** r_carrier->display_attributes( ).


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******* create RENTAL ***************************************** CREATE OBJECT r_rental EXPORTING im_name = ’HAPPY CAR RENTAL’.

******* create truck ***************************************** CREATE OBJECT r_truck EXPORTING im_make = ’MAN’ im_cargo = 45. r_rental->add_vehicle( r_truck ). ******* create truck *****************************************

Internal

Only

CREATE OBJECT r_bus EXPORTING im_make = ’Mercedes’ im_passengers = 80. r_rental->add_vehicle( r_bus ). ******* create truck ***************************************** CREATE OBJECT r_truck EXPORTING im_make = ’VOLVO’

Partner

im_cargo = 48. r_rental->add_vehicle( r_truck ).

Use

***** show attributes of rental *************************** r_rental->display_attributes( ).

SAP

*&---------------------------------------------------------------------* *&

Include

SAPBC401_VEHD_F

*

SAP

SAPBC401_VEHD_F

*&---------------------------------------------------------------------*

Use

* define interface lif_partners *---------------------------------------------------------------------* INTERFACE lif_partners.

Internal

METHODS display_partner. ENDINTERFACE.

Partner

*---------------------------------------------------------------------*

*---------------------------------------------------------------------* CLASS lcl_vehicle DEFINITION

*---------------------------------------------------------------------* CLASS lcl_vehicle DEFINITION.

PUBLIC SECTION. "------------------METHODS: get_average_fuel IMPORTING im_distance TYPE s_distance im_fuel TYPE ty_fuel RETURNING value(re_avgfuel) TYPE ty_fuel. METHODS

constructor IMPORTING im_make TYPE string.


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*

BC401


METHODS

display_attributes.

METHODS

set_make IMPORTING im_make TYPE string.

METHODS

get_make EXPORTING ex_make TYPE string.

CLASS-METHODS get_count EXPORTING re_count TYPE i.

PRIVATE SECTION.

DATA: make

TYPE string.

METHODS

init_make.

CLASS-DATA:

n_o_vehicles TYPE i.

"lcl_vehicle DEFINITION

ENDCLASS.

Partner

Internal

Only

"-------------------

*---------------------------------------------------------------------* CLASS lcl_vehicle IMPLEMENTATION

Use

*

*---------------------------------------------------------------------* * *---------------------------------------------------------------------*

SAP

METHOD get_average_fuel.

Use

METHOD constructor.

SAP

CLASS lcl_vehicle IMPLEMENTATION.

re_avgfuel = im_distance / im_fuel. "get_average_fuel

ENDMETHOD.

Partner

make = im_make. ADD 1 TO n_o_vehicles. "constructor

Internal

ENDMETHOD.

METHOD set_make. IF im_make IS INITIAL.

Only

" me->init_make( ). also possible

init_make( ). ELSE. make = im_make. ENDIF.

"set_make

ENDMETHOD.

METHOD init_make. make = ’default make’. ENDMETHOD.

"init_make


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METHOD get_make. ex_make = make. "get_make

ENDMETHOD.

METHOD display_attributes. WRITE: make. "display_attributes

ENDMETHOD.

re_count = n_o_vehicles. "get_count

ENDMETHOD.

"lcl_vehicle IMPLEMENTATION

*---------------------------------------------------------------------* *

CLASS lcl_truck DEFINITION

*---------------------------------------------------------------------* * *---------------------------------------------------------------------*

SAP

SAP

CLASS lcl_truck DEFINITION INHERITING FROM lcl_vehicle.

PUBLIC SECTION. "------------------METHODS:

constructor IMPORTING im_make TYPE string

Partner

Use

im_cargo TYPE ty_cargo.

Internal

Use

Partner

ENDCLASS.

Internal

Only

METHOD get_count.

METHODS

display_attributes REDEFINITION.

METHODS

get_cargo RETURNING value(re_cargo) TYPE ty_cargo.

PRIVATE SECTION. "-------------------

Only

DATA: max_cargo TYPE ty_cargo.

ENDCLASS.

*---------------------------------------------------------------------* *

CLASS lcl_truck IMPLEMENTATION

*---------------------------------------------------------------------* * *---------------------------------------------------------------------* CLASS lcl_truck IMPLEMENTATION.


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METHOD constructor. super->constructor( im_make ). max_cargo = im_cargo. "constructor

ENDMETHOD.

METHOD display_attributes. WRITE: / icon_ws_truck AS ICON.

Internal

Only

super->display_attributes( ). WRITE: 20 ’ Cargo = ’, max_cargo. ULINE. "display_attributes

ENDMETHOD.

Partner

METHOD get_cargo. re_cargo = max_cargo. "get_cargo

ENDMETHOD.

Use

ENDCLASS.

SAP

*

SAP

*---------------------------------------------------------------------* CLASS lcl_bus DEFINITION

*---------------------------------------------------------------------* * *---------------------------------------------------------------------*

Partner

Use

CLASS lcl_bus DEFINITION INHERITING FROM lcl_vehicle. PUBLIC SECTION. "------------------METHODS:

constructor IMPORTING im_make TYPE string

METHODS

display_attributes REDEFINITION.

Only

Internal

im_passengers TYPE i.

PRIVATE SECTION. "------------------DATA: max_passengers TYPE i.

ENDCLASS.

*---------------------------------------------------------------------* *

CLASS lcl_bus IMPLEMENTATION

*---------------------------------------------------------------------*


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* *---------------------------------------------------------------------* CLASS lcl_bus IMPLEMENTATION.

METHOD constructor. super->constructor( im_make ). max_passengers = im_passengers. "constructor

Internal

Only

ENDMETHOD.

METHOD display_attributes. WRITE: / icon_transportation_mode AS ICON. super->display_attributes( ). WRITE:

20 ’ Passengers = ’, max_passengers.

"display_attributes

ENDCLASS.

*---------------------------------------------------------------------* *

CLASS lcl_rental DEFINITION

SAP

* *---------------------------------------------------------------------* CLASS lcl_rental DEFINITION.

Partner

Use


constructor IMPORTING im_name TYPE string.

METHODS

add_vehicle IMPORTING im_vehicle

METHODS

display_attributes.

TYPE REF TO lcl_vehicle.

Internal

SAP

*---------------------------------------------------------------------*

Use

Partner

ULINE. ENDMETHOD.

INTERFACES lif_partners.

Only

PRIVATE SECTION. "------------------DATA: name TYPE string, vehicle_list TYPE TABLE OF REF TO lcl_vehicle. ENDCLASS.

*---------------------------------------------------------------------* *

CLASS lcl_rental IMPLEMENTATION

*---------------------------------------------------------------------*


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* *---------------------------------------------------------------------* CLASS lcl_rental IMPLEMENTATION. METHOD lif_partners~display_partner. display_attributes( ). ENDMETHOD.

METHOD constructor.

Internal

Only

name = im_name. "constructor

ENDMETHOD.

METHOD add_vehicle. APPEND im_vehicle TO vehicle_list. "add_vehicle

Partner

ENDMETHOD.

METHOD

display_attributes.

WRITE: / WRITE:

Use

DATA: r_vehicle TYPE REF TO lcl_vehicle. icon_transport_proposal AS ICON, name. ’ Here comes the vehicle list: ’. ULINE. ULINE.

LOOP AT vehicle_list INTO r_vehicle.

SAP

SAP

r_vehicle->display_attributes( ). ENDLOOP. "display_attributes

ENDMETHOD.

"lcl_rental IMPLEMENTATION

Partner

Use

ENDCLASS.

SAPBC401_INTS_A *&---------------------------------------------------------------------*

Internal

*&

Include

SAPBC401_INTS_A

*

*&---------------------------------------------------------------------*

*


Only

*------------------------------------------------------------------* *

*------------------------------------------------------------------* ... *------------------------------------------------------------------* *


*

*------------------------------------------------------------------* ... *---------------------------------------------------------------------*


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*

BC401


*

*---------------------------------------------------------------------* ... *---------------------------------------------------------------------* *


*

*---------------------------------------------------------------------* ...

*


*

*---------------------------------------------------------------------* ...

*


*

*---------------------------------------------------------------------* ... *---------------------------------------------------------------------* *


*

SAP

* ... *---------------------------------------------------------------------* CLASS lcl_carrier DEFINITION.

Partner

Use

PUBLIC SECTION. "---------------------------------------INTERFACES lif_partners. METHODS: constructor IMPORTING im_name TYPE string, get_name RETURNING value(ex_name) TYPE string,

Internal

SAP

*---------------------------------------------------------------------*

Use

Partner

*---------------------------------------------------------------------*

Internal

Only

*---------------------------------------------------------------------*

add_airplane IMPORTING im_plane TYPE REF TO lcl_airplane,

Only

display_airplanes, display_attributes. PRIVATE SECTION. "----------------------------------DATA: name

TYPE string,



*---------------------------------------------------------------------* *

CLASS lcl_carrier IMPLEMENTATION


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*---------------------------------------------------------------------* CLASS lcl_carrier IMPLEMENTATION. METHOD lif_partners~display_partner. display_airplanes( ). "lif_partners~display_partner

ENDMETHOD.

METHOD add_airplane. ENDMETHOD.

Internal

Only

APPEND im_plane TO airplane_list. "add_airplane

METHOD display_attributes. WRITE: icon_flight AS ICON, name . ULINE. ULINE.

Partner

display_airplanes( ). ENDMETHOD.

"display_attributes

Use

METHOD display_airplanes. DATA: r_plane TYPE REF TO lcl_airplane. LOOP AT airplane_list INTO r_plane. r_plane->display_attributes( ).

SAP

ENDMETHOD.

SAP

ENDLOOP. "display_airplanes

METHOD constructor. name = im_name.

Use

Partner

ENDMETHOD.

"constructor

METHOD get_name. ex_name = name.

Internal

ENDMETHOD.

ENDCLASS.

"get_name


Only

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Use

Partner

Only

Internal

SAP

SAP Only

Internal

Use

Partner

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Exercise 15: Aggregation, Generic Calls, and Polymorphism Exercise Objectives

Only Partner SAP

1.


2.

If necessary, add a class LCL_TRAVEL_AGENCY that uses the interface LIF_PARTNERS to your UML diagram.

Use

3.

From program SAPBC401_VEHT_B, copy the portions of the source text for the local class LCL_TRAVEL_AGENCY into your main program or one of your include programs to extend them there.

4.

Add to the row type of the internal table PARTNER_LIST so that references to the business partners that have implemented your interface can be buffered.

5.

Add to the signature and implementation of method ADD_PARTNER so that the business partner references can be added to the list PARTNER_LIST.

6.

Add to the implementation of method DISPLAY_AGENCY_PARTNERS so that the attributes of all business partners of the travel agency can be added to the list. The centrally provided method DISPLAY_PARTNER needs to be called for each business partner.

Use

You now need to add a user class to your program: Travel agencies need to manage various business partners using the interface and access the business partners’ general services.

Internal

Business Example

Task 1: Define a local class for travel agencies.

Only

255

Partner


SAP


08-03-2004

Internal

After completing this exercise, you will be able to: • Realize aggregation relationships between classes • Program narrowing cast assignments • Use inheritance relationships for polymorphic method calls


BC401

Task 2:

In the main program, define a suitably typed reference variable for your new travel agency class.

2.

Using the reference, generate an instance of your class LCL_TRAVEL_AGENCY. Decide for yourself how to fill the attributes.

3.

Call the method ADD_PARTNER to transfer the references to the generated airline and car rental company instances to the travel agency.

4.

Add the attributes of the travel agency by calling its method DISPLAY_AGENCY_PARTNERS.

Use

Partner

1.

Internal

Only

In the main program, generate a travel agency instance, transfer the references to the airline and car rental company to this instance, and add the attributes.

SAP

SAP Only

Internal

Use

Partner

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Solution 15: Aggregation, Generic Calls, and Polymorphism Task 1: Define a local class for travel agencies. Complete your ZBC401_##_MAIN program or copy the sample solution from the previous exercise. (Where ## is your two-digit group number). a) b)

If necessary, add a class LCL_TRAVEL_AGENCY that uses the interface LIF_PARTNERS to your UML diagram. a)

3.

From program SAPBC401_VEHT_B, copy the portions of the source text for the local class LCL_TRAVEL_AGENCY into your main program or one of your include programs to extend them there.


Add to the implementation of method DISPLAY_AGENCY_PARTNERS so that the attributes of all business partners of the travel agency can be added to the list. The centrally provided method DISPLAY_PARTNER needs to be called for each business partner.

SAP Use

a)



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Only

Internal

Add to the signature and implementation of method ADD_PARTNER so that the business partner references can be added to the list PARTNER_LIST. a)

6.


Partner

Add to the row type of the internal table PARTNER_LIST so that references to the business partners that have implemented your interface can be buffered. a)

5.


SAP

a) 4.

Speak to your instructor if you have any questions.

Use

Partner

2.

Carry out this step in the usual manner. Additional information is available in the SAP Library. Model solution: SAPBC401_INTS_MAIN_B

Internal

Only

1.


BC401

Task 2: In the main program, generate a travel agency instance, transfer the references to the airline and car rental company to this instance, and add the attributes. 1.

In the main program, define a suitably typed reference variable for your new travel agency class. a)

Using the reference, generate an instance of your class LCL_TRAVEL_AGENCY. Decide for yourself how to fill the attributes. a)

Call the method ADD_PARTNER to transfer the references to the generated airline and car rental company instances to the travel agency. a)

4.


Add the attributes of the travel agency by calling its method DISPLAY_AGENCY_PARTNERS. a)

Use

Partner

3.



SAP

SAP


Use

Partner

SAPBC401_INTS_MAIN_B REPORT

sapbc401_ints_main_b.

TYPES ty_fuel TYPE p DECIMALS 2. TYPES ty_cargo TYPE p DECIMALS 2.

Internal

Internal

Only

2.


TYPE-POOLS icon.

Only

INCLUDE sapbc401_vehd_g. INCLUDE sapbc401_ints_a. DATA: r_plane TYPE REF TO lcl_airplane, r_cargo TYPE REF TO lcl_cargo_plane, r_passenger TYPE REF TO lcl_passenger_plane, r_carrier TYPE REF TO lcl_carrier, r_agency TYPE REF TO lcl_travel_agency, r_rental TYPE REF TO lcl_rental,


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r_truck TYPE REF TO lcl_truck, r_bus TYPE REF TO lcl_bus.


***** Create TRAVEL_AGENCY **************************************

Internal

Only

CREATE OBJECT r_agency EXPORTING im_name = ’Fly&Smile Travel’.

***** Create CARRIER ********************************************

Partner

CREATE OBJECT r_carrier EXPORTING im_name = ’Smile&Fly Travel’. ... ***** insert business-parnter of agency into partner_list***********

Use

r_agency->add_partner( r_carrier ).

******* create RENTAL *****************************************

SAP

SAP

CREATE OBJECT r_rental EXPORTING im_name = ’HAPPY CAR RENTAL’.

... ***** insert business-parnter of agency into partner_list***********

Partner

Use

r_agency->add_partner( r_rental ).

******* show attributes of all partners of travel_agency ******

Internal

r_agency->display_agency_partners( ).

SAPBC401_VEHD_G

Only

*---------------------------------------------------------------------* * define client lcl_travel_agency * it will use the interface lif_partners *---------------------------------------------------------------------* INTERFACE lif_partners. METHODS display_partner. ENDINTERFACE.

"lif_partners

... *---------------------------------------------------------------------*


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*

BC401


*---------------------------------------------------------------------* * *---------------------------------------------------------------------* CLASS lcl_rental DEFINITION. PUBLIC SECTION. METHODS:


METHODS

add_vehicle IMPORTING im_vehicle

METHODS

display_attributes.

Internal

Only

"-------------------

TYPE REF TO lcl_vehicle. INTERFACES: lif_partners. "------------------DATA: name TYPE string, vehicle_list TYPE TABLE OF REF TO lcl_vehicle. ENDCLASS.

"lcl_rental DEFINITION

*---------------------------------------------------------------------*

SAP


*---------------------------------------------------------------------* * *---------------------------------------------------------------------*

SAP

*

Use

Partner

PRIVATE SECTION.

...

Use

*

CLASS lcl_travel_agency DEFINITION

*---------------------------------------------------------------------* *

Internal

*---------------------------------------------------------------------* CLASS lcl_travel_agency DEFINITION.

Only



METHODS

add_partner IMPORTING im_partner TYPE REF TO lif_partners.

METHODS

display_agency_partners.

PRIVATE SECTION. "------------------DATA: name TYPE string, partner_list TYPE TABLE OF REF TO lif_partners.


260


Partner

*---------------------------------------------------------------------*

08-03-2004

BC401


ENDCLASS.

"lcl_travel_agency DEFINITION

*---------------------------------------------------------------------* *

CLASS lcl_travel_agency IMPLEMENTATION

*---------------------------------------------------------------------* * *---------------------------------------------------------------------* CLASS lcl_travel_agency IMPLEMENTATION.

Internal

Only

METHOD display_agency_partners. DATA: r_partner TYPE REF TO lif_partners. WRITE: icon_dependents AS ICON, name. WRITE:

’ Here are the partners of the travel agency: ’.

ULINE.

Partner

ULINE. LOOP AT partner_list INTO r_partner. r_partner->display_partner( ).

ENDMETHOD.

METHOD

Use

ENDLOOP. "display_agency_partners

constructor.

SAP

ENDMETHOD. METHOD

SAP

name = im_name. "constructor

add_partner.

APPEND im_partner TO partner_list.

Use

"add_partner "lcl_travel_agency IMPLEMENTATION

Only

Internal

ENDCLASS.

Partner

ENDMETHOD.

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BC401

Lesson Summary

Only

Related Information

Use

Partner


Internal

You should now be able to: • Define and implement interfaces • Implement interface methods • Use interface references to make narrowing cast assignments • Use interface references to make widening cast assignments • Explain the term polymorphism with reference to interfaces • Use cast assignments with interfaces to make generic calls

SAP

SAP Only

Internal

Use

Partner

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Lesson: Events

Lesson: Events Lesson Overview

Internal

Only

This lesson provides a general introduction to the concept of events in object orientation, followed by an explanation of all related modeling aspects and syntax elements. The section entitled ’Registration’ contains the information that is probably most important for understanding the topic.


Partner

Define and trigger events Handle events Register and deregister event handling Explain the key differences between explicit method calls and event-controlled method calls

Use

• • • •

You want to implement event-controlled behavior from your model in ABAP Objects.

Use Internal

Besides attributes and methods, classes – and their instances – can contain a third type of component: events. Instance events can be triggered by the instances of the class, while static instance events can be triggered by the class itself. Events can also be defined as interface components.

Partner

Event-Controlled Method Calls

SAP

SAP

Business Example

Only

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263

BC401

Internal

Figure 126: Event-Controlled Method Calls

SAP Use

An event can have exporting parameters, meaning that, unlike in the explicit method call, the calling program determines the protocol. In this application example, after an instance in the “vehicle” class is created, it triggers the event “vehicle created.” This event is received by different instances and processed differently be each one. The rental car company considers purchasing a vehicle, while the vehicle registration office registers the car, and so on.

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Internal

Because of the definition of the handler method, the range of possible results can be narrowed down, but which, if any, of these results actually will occur can only be determined after the event has been triggered.

Partner

This results in a completely different modeling concept: While you are developing the class that triggers the event, you do not need to know anything about the class that is handling it. The triggering class sends a specific message to all classes (and if need be, their instances) of the running program. At the time of development, it is completely unclear what type of handlers there will be and how many will be used.

SAP

Given the right circumstances, handler methods can now react to the triggering of this event. This means that the runtime system calls the handler methods after the event has been triggered. That is, the handler method is not called directly by the client.

Use

Partner

Only


BC401

Lesson: Events

Caution: Do not confuse this concept of events in object-oriented programming with events in the ABAP runtime system (LOAD-OF-PROGRAM, START-OF-SELECTION, and so on). Also do not confuse it with background processing or workflow controlling.

Use

Partner

Only

Internal

Figure 127: Event Handling in a UML Class Diagram

Partner

SAP Use

SAP

In UML class diagrams, a dotted arrow with the stereotype «handlesEventOf» points from the handling class to the triggering class. The event definition and signature only appear implicitly in the handling class within the handler method. The handler methods are separated from the other methods using the stereotype «eventHandler».

Triggering and Handling events

Only

Internal

The following summarizes all of the required programming steps for event-controlling. They will be explained in more detail later.

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BC401

Keep in mind that, depending on the status of your application, you may not need to program all steps. The separation of cause and effect in your programming should be reflected in the way you construct complex applications. Often, the event is already triggered and all you have to do is create another event handler.

Use

Partner

Figure 128: Triggering and Handling Events – Overview

Internal

Only


SAP

SAP Only

Internal

Use

Partner

Figure 129: Defining and Triggering Events Syntax

Within a class, instance events are defined using the EVENTS statement, while static events are defined using the CLASS-EVENTS statement.

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Lesson: Events

Events can only have exporting parameters, which must be passed by value as a copy. A class or instance can trigger an event at runtime using the RAISE EVENT statement. Both instance events and static events can be triggered in instance methods. Only static events can be triggered in static methods. When an event is triggered, the handler methods that are registered to this event are called in sequence. Of course, these can trigger more events of their own.

Use

Partner

Only

Internal

If the event contains exporting parameters and you want to be able to address these syntactically, you must have specified the exporting parameters immediately after IMPORTING in the definition of the method. The handler method’s signature can consist of no more than the exporting parameters of the associated event. The parameters are typed by the handler method during the definition of the event. (“The object that triggers the event determines the protocol.”) In addition to the explicitly defined exporting parameters, the predefined importing parameter SENDER can always be listed. By using that parameter, you can place a reference to the event-trigger object into the handler method.

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Only

Internal

Instance events or static methods can be defined within a class to handle events. To do so, you must specify the event (FOR EVENT) and the class or interface in which the event was defined (OF).

Partner

Use

SAP

SAP

Figure 130: Handling Events – Syntax


BC401

Therefore, handler methods are usually called by triggered events (RAISE EVENT): However, they can be called explicitly as well (CALL METHOD).

Registering for Events

Use

Partner

When triggering instance events, you also have to specify what event the reaction will trigger. If instance methods are set to carry out the reaction, you also have to specify which instance(s) will perform the reaction.

Internal

Only

The definition of the handler method only specifies how and to which event of which class the method will react. At runtime, it needs to be determined which possible reactions will actually take place and when each of these will happen.

Internal

In this example, handler methods are defined for the event of the vehicle class, the car rental class, and the vehicle registration class. However, you can only predetermine which car rental instances and vehicle registration instances will react to which vehicle instance, and when they will do so. Registrations can also be revoked.

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Only

These specifications are collectively known as registration. The registration is always carried out using the trigger. When the event is triggered, the runtime uses the registrations of the trigger to determine which event handler methods need to be called.

Partner

Use

SAP

SAP

Figure 131: Registering Event Handling

BC401

Lesson: Events

Use

Partner

Only

Internal

Figure 132: Registering Event Handling – Syntax

SAP Use

The addition ACTIVATION ’X’ is optional. To revoke the registration,

Internal

use ACTIVATION space.

Only

You can register several methods with one SET-HANDLER statement:

SET HANDLER ref_handler_1->on_eventname_1 ... ref_handler_n->on_eventname_n FOR ... .

08-03-2004


Partner

With instance events, FOR is followed by the reference to the object that triggers the event. Alternatively, you can also use the addition ALL INSTANCES. That way, you can also register objects that have not yet been created.

SAP

Events are registered using the SET HANDLER statement. Registration is only active at program runtime.

269


BC401

If multiple methods were registered to one event, then the sequence in which the event handler methods are called is not defined, that is, there is no guaranteed sequence in which the event handler methods are called. If a new event handler is registered within an event handler method for an event that has just been triggered, then this event handler is added to the end of the sequence and is then also executed when its turn comes. If an existing event handler is deregistered in an event handler method, then this handler is deleted from the event handler method sequence.

Use

Partner

Only

Internal

Internal

Objects that are registered for event handling are not deleted by the Garbage Collector if there are no remaining references to them.

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Every object or class that has defined events has an internal table: the handler table. All handler methods that are registered to the various events are listed within the table. For instance methods, the handler table also contains references to the registered objects.

Partner

Use

SAP

SAP

Figure 133: Registration/Deregistration – Handler Tables

BC401

Lesson: Events

Visibility Sections in Event Handling Events are also subject to the visibility concept and can therefore be either public, protected, or private. Event handler methods also have visibility attributes. •

The visibility of an event controls “who” may handle the event.

Only

•

PRIVATE Can only be handled within its class The visibility of a handler method controls the authorization required for registering the method, that is, the locations at which the SET HANDLER statement may be programmed.

SAP

SAP

PUBLIC Anywhere in the program PROTECTED Can be handled by users within that class or its subclasses

Only

Internal

Event handler methods can only have the same visibility or more restricted visibility than the events they refer to.

Partner

PRIVATE Can only be handled within its class

Use

Use

Partner

PROTECTED Can only be handled by users within that class or its subclasses

Internal

PUBLIC All

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BC401

Use

Partner

Only

Internal

SAP

SAP Only

Internal

Use

Partner

272


08-03-2004

BC401

Lesson: Events

Exercise 16: Events in Superclasses Exercise Objectives

Business Example

Task 1:

Complete your program ZBC401_##_MAIN program or copy the program SAPBC401_INTS_MAIN_B (where ## is your two-digit group number).

2.

Remove the calls of the method ADD_AIRPLANE from your main program. Note: The entry of an airplane reference into the airline’s list is to be event-controlled. Identify the class that is suitable for triggering the event and the classes that should be used for handling the event. Use your UML diagram if necessary. If applicable, illustrate the relationships in your UML diagram.

4.

Define the public event AIRPLANE_CREATED and trigger it in the class LCL_AIRPLANE using a suitable method.

5.

Change the method ADD_AIRPLANE in class LCL_CARRIER into a handler method for the event that you just defined. You will need to change both the signature and the implementation.


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273

Only

Internal

3.

Partner

Use

1.

SAP

SAP

Define an event for the creation of an airplane. Trigger and handle it so that the reference to the airplane is entered into the airline’s list of airplanes.

Use

Partner

Airplane and vehicle references are to be included in the airline and the car rental company’s lists. This process is to be event-controlled.

Internal

Only

After completing this exercise, you will be able to: • Define and trigger events • Handle events • Register event handling


6.

BC401

Register the new handler method, so that the airline enters every airplane that was created after itself in the list. Note: Although this model is unrealistic, we will use it for the time being. A different rule for entering the airplane can be created later.

7.

Observe the execution of the program in the ABAP Debugger.

1.

Remove the calls of the method ADD_VEHICLE from your main program.

2.

Define the event VEHICLE_CREATED and proceed as you did in the previous exercise.

Use

Only Partner

Define an event for the creation of a vehicle. Trigger and handle it so that the reference to the vehicle is entered into the car rental company’s list of vehicles.

Internal

Task 2:

SAP

SAP Only

Internal

Use

Partner

274


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BC401

Lesson: Events

Solution 16: Events in Superclasses Task 1: Define an event for the creation of an airplane. Trigger and handle it so that the reference to the airplane is entered into the airline’s list of airplanes. Complete your program ZBC401_##_MAIN program or copy the program SAPBC401_INTS_MAIN_B (where ## is your two-digit group number). a)

Partner

Note: The entry of an airplane reference into the airline’s list is to be event-controlled. a)


Identify the class that is suitable for triggering the event and the classes that should be used for handling the event. Use your UML diagram if necessary.

Use

a)

Define the public event AIRPLANE_CREATED and trigger it in the class LCL_AIRPLANE using a suitable method. a)

5.


Change the method ADD_AIRPLANE in class LCL_CARRIER into a handler method for the event that you just defined. You will need to change both the signature and the implementation. a)



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275

Only

Internal

4.


Partner

If applicable, illustrate the relationships in your UML diagram.

SAP

3.

Remove the calls of the method ADD_AIRPLANE from your main program.

Use

2.

SAP

b)

Carry out this step in the usual manner. Additional information is available in the SAP Library. Model solution: SAPBC401_EVES_MAIN_A

Internal

Only

1.


6.

BC401

Register the new handler method, so that the airline enters every airplane that was created after itself in the list. Note: Although this model is unrealistic, we will use it for the time being. A different rule for entering the airplane can be created later. a)

Only

Observe the execution of the program in the ABAP Debugger. a)


Define an event for the creation of a vehicle. Trigger and handle it so that the reference to the vehicle is entered into the car rental company’s list of vehicles. 1.

Remove the calls of the method ADD_VEHICLE from your main program. a)

SAP


Define the event VEHICLE_CREATED and proceed as you did in the previous exercise.

Use

Speak to your instructor if you have any questions. See the source code extract from the model solution

Partner

a) b)

Result

Internal


SAPBC401_EVES_MAIN_A sapbc401_eves_main_a.

Only

REPORT

TYPES: ty_fuel TYPE p DECIMALS 2, ty_cargo TYPE p DECIMALS 2.

TYPE-POOLS icon. INCLUDE sapbc401_vehd_h. INCLUDE sapbc401_eves_a.


276


SAP

2.

Use

Partner

Task 2:

Internal

7.


08-03-2004

BC401

Lesson: Events

DATA: r_vehicle TYPE REF TO lcl_vehicle, r_truck TYPE REF TO lcl_truck, r_bus

TYPE REF TO lcl_bus,

r_passenger TYPE REF TO lcl_passenger_plane, r_cargo TYPE REF TO lcl_cargo_plane, r_carrier TYPE REF TO lcl_carrier, r_rental TYPE REF TO lcl_rental,

Internal

Only

r_agency TYPE REF TO lcl_travel_agency.

START-OF-SELECTION. *########################

Partner

***** Create TRAVEL_AGENCY ************************************** CREATE OBJECT r_agency EXPORTING im_name = ’Fly&Smile Travel’.

Use

***** Create CARRIER ******************************************** CREATE OBJECT r_carrier EXPORTING im_name = ’Smile&Fly Travel’.

SAP

SAP

***** Passenger Plane ******************************************** CREATE OBJECT r_passenger EXPORTING im_name = ’LH BERLIN’ im_planetype = ’747-400’ im_seats = 345.

Partner

Use

***** cargo Plane ************************************************ CREATE OBJECT r_cargo EXPORTING im_name = ’US Hercules’ im_planetype = ’747-500’

Internal

im_cargo = 533.

***** insert business-parnter of agency into partner_list***********

Only

r_agency->add_partner( r_carrier ).

******* create RENTAL ***************************************** CREATE OBJECT r_rental EXPORTING im_name = ’HAPPY CAR RENTAL’. ******* create truck ***************************************** CREATE OBJECT r_truck EXPORTING im_make = ’MAN’ im_cargo = 45.


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BC401

******* create truck ***************************************** CREATE OBJECT r_bus EXPORTING im_make = ’Mercedes’ im_passengers = 80.

******* create truck ***************************************** CREATE OBJECT r_truck EXPORTING im_make = ’VOLVO’ im_cargo = 48.

Internal

Only

***** insert business-parnter of agency into partner_list*********** r_agency->add_partner( r_rental ). ******* show attributes of all partners of travel_agency ******

SAPBC401_VEHD_H *&---------------------------------------------------------------------* *&

Include

SAPBC401_VEHD_H

*

*&---------------------------------------------------------------------* *---------------------------------------------------------------------*

Use

Partner


* it will use the interface lif_partners *---------------------------------------------------------------------* INTERFACE lif_partners.

SAP

SAP

* define client lcl_travel_agency

METHODS display_partner.

Use

"lif_partners

*---------------------------------------------------------------------* *

CLASS lcl_vehicle DEFINITION

Internal

*---------------------------------------------------------------------* CLASS lcl_vehicle DEFINITION.

Only

PUBLIC SECTION. "------------------METHODS: get_average_fuel IMPORTING im_distance TYPE s_distance im_fuel TYPE ty_fuel RETURNING value(re_avgfuel) TYPE ty_fuel. METHODS

constructor IMPORTING im_make TYPE string.

METHODS

display_attributes.

METHODS

set_make IMPORTING im_make TYPE string.

METHODS

get_make EXPORTING ex_make TYPE string.

CLASS-METHODS get_count EXPORTING re_count TYPE i.


278


Partner

ENDINTERFACE.

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BC401

Lesson: Events

EVENTS: vehicle_created. PRIVATE SECTION. DATA: make

TYPE string.

METHODS

init_make.

CLASS-DATA:

n_o_vehicles TYPE i.

ENDCLASS.

Internal

Only

"-------------------

"lcl_vehicle DEFINITION

*---------------------------------------------------------------------* *

CLASS lcl_vehicle IMPLEMENTATION

Partner

*---------------------------------------------------------------------* * *---------------------------------------------------------------------*

Use

CLASS lcl_vehicle IMPLEMENTATION. METHOD get_average_fuel. re_avgfuel = im_distance / im_fuel. "get_average_fuel

SAP

SAP

ENDMETHOD. METHOD constructor. make = im_make. ADD 1 TO n_o_vehicles. RAISE EVENT vehicle_created.

Use

Partner

ENDMETHOD.

"constructor

METHOD set_make. IF im_make IS INITIAL.

Internal

init_make( ).

" me->init_make( ). also possible

ELSE. make = im_make.

Only

ENDIF. ENDMETHOD.

"set_make

METHOD init_make. make = ’default make’. ENDMETHOD.

"init_make

METHOD get_make. ex_make = make. ENDMETHOD.

"get_make


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BC401

METHOD display_attributes. WRITE: make. ENDMETHOD.

"display_attributes

METHOD get_count. re_count = n_o_vehicles. "get_count

ENDCLASS.

"lcl_vehicle IMPLEMENTATION

*---------------------------------------------------------------------* CLASS lcl_truck DEFINITION

*---------------------------------------------------------------------* * *---------------------------------------------------------------------* ...

*---------------------------------------------------------------------*

SAP

CLASS lcl_bus DEFINITION

*---------------------------------------------------------------------* * *---------------------------------------------------------------------*

SAP

*

Use

Partner

*

Internal

Only

ENDMETHOD.

*---------------------------------------------------------------------* *


*---------------------------------------------------------------------*

Internal

* *---------------------------------------------------------------------*

Partner

Use

...

CLASS lcl_rental DEFINITION.

Only



METHODS

add_vehicle FOR EVENT vehicle_created OF lcl_vehicle

METHODS

display_attributes.

IMPORTING sender.

INTERFACES: lif_partners. PRIVATE SECTION. "-------------------


280


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Lesson: Events

DATA: name TYPE string, vehicle_list TYPE TABLE OF REF TO lcl_vehicle. ENDCLASS.


*---------------------------------------------------------------------* *


*---------------------------------------------------------------------* *

Internal

Only

*---------------------------------------------------------------------* CLASS lcl_rental IMPLEMENTATION. METHOD lif_partners~display_partner. display_attributes( ).

Partner

ENDMETHOD. METHOD

"lif_partners~display_partner

constructor.

name = im_name. ENDMETHOD.

METHOD

Use

SET HANDLER add_vehicle FOR ALL INSTANCES. "constructor

add_vehicle.

SAP

ENDMETHOD. METHOD

SAP

APPEND sender TO vehicle_list. "add_vehicle

display_attributes.

DATA: r_vehicle TYPE REF TO lcl_vehicle.

Use

WRITE:

Partner

WRITE: /

icon_transport_proposal AS ICON, name. ’ Here comes the vehicle list: ’. ULINE. ULINE.

LOOP AT vehicle_list INTO r_vehicle. r_vehicle->display_attributes( ).

ENDCLASS.

"display_attributes

Only

Internal

ENDLOOP. ENDMETHOD.


*---------------------------------------------------------------------* *

CLASS lcl_travel_agency DEFINITION

*---------------------------------------------------------------------* * *---------------------------------------------------------------------* ...


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BC401

SAPBC401_EVES_A *&---------------------------------------------------------------------* *&

Include

SAPBC401_EVES_A

*

*&---------------------------------------------------------------------* *------------------------------------------------------------------* *


*

*------------------------------------------------------------------*

Internal

Only

CLASS lcl_airplane DEFINITION. PUBLIC SECTION. "--------------------------------------------CONSTANTS: pos_1 TYPE i VALUE 30.

Partner


TYPE string


Use


SAP

SAP

EVENTS airplane_created.

PRIVATE SECTION. "---------------------------------------------IMPORTING im_type


EXPORTING ex_weight

TYPE s_plan_wei

ex_tankcap

Internal

DATA: name

Partner

Use

METHODS: get_technical_attributes

TYPE s_capacity.

TYPE string,


ENDCLASS.

Only


*------------------------------------------------------------------* *


*


METHOD constructor.


282


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BC401

Lesson: Events

name

= im_name.

planetype

= im_planetype.

n_o_airplanes = n_o_airplanes + 1. RAISE EVENT airplane_created. ENDMETHOD.

"constructor

METHOD display_attributes. DATA: weight TYPE saplane-weight,

Internal

Only

cap TYPE saplane-tankcap. WRITE: / icon_ws_plane AS ICON, / ’Name of Airplane:’(001), AT pos_1 name, / ’Type of airplane: ’(002), AT pos_1 planetype. get_technical_attributes( EXPORTING im_type = planetype

Partner

IMPORTING ex_weight = weight ex_tankcap = cap ). WRITE: / ’Gewicht:’(003), weight, ENDMETHOD.

Use

’Tankkap:’(004), cap. "display_attributes

METHOD display_n_o_airplanes.

SAP

SAP

WRITE: /, / ’Number of airplanes: ’(ca1), AT pos_1 n_o_airplanes LEFT-JUSTIFIED, /. ENDMETHOD.


METHOD get_technical_attributes.

Partner

Use

SELECT SINGLE weight tankcap FROM saplane INTO (ex_weight, ex_tankcap) WHERE planetype = im_type. IF sy-subrc 0.

Internal

ex_weight = 100000. ex_tankcap = 10000. ENDIF.

ENDCLASS.

Only

ENDMETHOD.

"get_technical_attributes "lcl_airplane IMPLEMENTATION

*---------------------------------------------------------------------* *


*---------------------------------------------------------------------* * *---------------------------------------------------------------------*


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283


BC401

... *---------------------------------------------------------------------* *


*---------------------------------------------------------------------* * *---------------------------------------------------------------------* ... *---------------------------------------------------------------------* CLASS lcl_carrier DEFINITION

*---------------------------------------------------------------------* * *---------------------------------------------------------------------*

Partner

CLASS lcl_carrier DEFINITION. PUBLIC SECTION. "----------------------------------------

Use

INTERFACES lif_partners. METHODS: constructor IMPORTING im_name TYPE string, get_name RETURNING value(ex_name) TYPE string, add_airplane FOR EVENT airplane_created OF lcl_airplane

SAP

IMPORTING sender,

SAP

Internal

Only

*

display_airplanes, display_attributes. PRIVATE SECTION. "-----------------------------------

Use

TYPE string,



Internal

*---------------------------------------------------------------------* *


Partner

DATA: name

*---------------------------------------------------------------------*

Only

CLASS lcl_carrier IMPLEMENTATION. METHOD lif_partners~display_partner. display_airplanes( ). ENDMETHOD.


METHOD add_airplane. APPEND sender TO airplane_list. ENDMETHOD.

"add_airplane



284


08-03-2004

BC401

Lesson: Events

WRITE: icon_flight AS ICON, name . ULINE. ULINE. display_airplanes( ). ENDMETHOD.

"display_attributes

METHOD display_airplanes. DATA: r_plane TYPE REF TO lcl_airplane. LOOP AT airplane_list INTO r_plane. r_plane->display_attributes( ). ENDMETHOD.

Internal

Only

ENDLOOP. "display_airplanes

METHOD constructor. SET HANDLER add_airplane FOR ALL INSTANCES.

Partner

name = im_name. ENDMETHOD.

"constructor

Use



SAP

SAP

ENDCLASS.

"get_name

Only

Internal

Use

Partner

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285


BC401

Use

Partner

Only

Internal

SAP

SAP Only

Internal

Use

Partner

286


08-03-2004

BC401

Lesson: Events

Exercise 17: Events in Interfaces (optional) Exercise Objectives

Only

Business Example

Partner

Task:

SAP Use


2.

Remove the calls of the method ADD_PARTNER from your main program.

3.

If necessary, examine your UML diagram. Which class or interface should define the event? Which class or interface should trigger it? Which class or interface should handle it?

Only

Internal

Note: The entry of a business partner reference into the travel agent’s list is to be event-controlled.

If applicable, illustrate the relationships in your UML diagram. 4.

Define the event PARTNER_CREATED and trigger it using a suitable method in the class that you selected.


08-03-2004


Partner

1.

SAP

Define an event for the creation of a business partner. Trigger and handle it so that the reference to the business partner is entered into the travel agent’s list of partners.

Use

Airline and car rental company references are to be entered into the travel agent’s list. This process is to be event-controlled. Be sure to create your program so that it can be easily extended to manage additional business partners of the travel agent in the future.

Internal

After completing this exercise, you will be able to: • Define events in interfaces • Trigger interface events in implementing classes • Handle interface events • Register event handling

287


BC401

5.

Change the method ADD_PARTNER in the class LCL_TRAVEL_AGENCY into a handler method for the event that you just defined. You will need to change both the signature and the implementation.

6.

Register the new handler method, so that the travel agent enters every business partner that was created after itself into the list.

Only

Observe the execution of the program in the ABAP Debugger.

Use

Partner

7.

Internal

Note: Although this model is unrealistic, we will use it for the time being. A different rule for entering the business partner can be created later.

SAP

SAP Only

Internal

Use

Partner

288


08-03-2004

BC401

Lesson: Events

Solution 17: Events in Interfaces (optional) Task: Define an event for the creation of a business partner. Trigger and handle it so that the reference to the business partner is entered into the travel agent’s list of partners. Complete your ZBC401_##_MAIN program or copy the sample solution from the previous exercise. (Where ## is your two-digit group number). a)

Partner

3.

Remove the calls of the method ADD_PARTNER from your main program. Note: The entry of a business partner reference into the travel agent’s list is to be event-controlled. a)


SAP

If necessary, examine your UML diagram. Which class or interface should define the event? Which class or interface should trigger it? Which class or interface should handle it?

Use

Define the event PARTNER_CREATED and trigger it using a suitable method in the class that you selected. a)

5.


Change the method ADD_PARTNER in the class LCL_TRAVEL_AGENCY into a handler method for the event that you just defined. You will need to change both the signature and the implementation. a)



08-03-2004


289

Only

Internal

4.


Partner

If applicable, illustrate the relationships in your UML diagram. a)

Use

2.

SAP

b)

Carry out this step in the usual manner. Additional information is available in the SAP Library. Model solution: SAPBC401_EVES_MAIN_B

Internal

Only

1.


6.

BC401

Register the new handler method, so that the travel agent enters every business partner that was created after itself into the list. Note: Although this model is unrealistic, we will use it for the time being. A different rule for entering the business partner can be created later. a)

Only

Observe the execution of the program in the ABAP Debugger. a)


Partner


REPORT

Use

SAPBC401_EVES_MAIN_B sapbc401_eves_main_b.

SAP

SAP


Use

DATA: r_vehicle TYPE REF TO lcl_vehicle,

Partner

Internal

TYPE-POOLS icon. INCLUDE sapbc401_vehd_i. INCLUDE sapbc401_eves_b.

r_truck TYPE REF TO lcl_truck, r_bus


Only

r_passenger TYPE REF TO lcl_passenger_plane, r_cargo TYPE REF TO lcl_cargo_plane, r_carrier TYPE REF TO lcl_carrier, r_rental TYPE REF TO lcl_rental, r_agency TYPE REF TO lcl_travel_agency.



290

Internal

7.



08-03-2004

BC401

Lesson: Events

******* create travel_agency ***************************************** CREATE OBJECT r_agency EXPORTING im_name = ’Fly&Smile Travel’.

******* create rental ***************************************** CREATE OBJECT r_rental EXPORTING im_name = ’HAPPY CAR RENTAL’.

Internal

Only

******* create truck ***************************************** CREATE OBJECT r_truck EXPORTING im_make = ’MAN’ im_cargo = 45. ******* create truck ***************************************** CREATE OBJECT r_bus EXPORTING im_make = ’Mercedes’

Partner

im_passengers = 80. ******* create truck *****************************************

Use

CREATE OBJECT r_truck EXPORTING im_make = ’VOLVO’ im_cargo = 48.

***** Create CARRIER ********************************************

SAP

SAP

CREATE OBJECT r_carrier EXPORTING im_name = ’Smile&Fly Travel’.

***** Passenger Plane ******************************************** CREATE OBJECT r_passenger EXPORTING im_name = ’LH BERLIN’

Partner

Use

im_planetype = ’747-400’ im_seats = 345. ***** cargo Plane ************************************************ CREATE OBJECT r_cargo EXPORTING

Internal

im_name = ’US Hercules’ im_planetype = ’747-500’ im_cargo = 533.

Only

******* show attributes of all partners of travel_agency ****** r_agency->display_agency_partners( ).

SAPBC401_VEHD_I *&---------------------------------------------------------------------* *&

Include

SAPBC401_VEHD_I

*

*&---------------------------------------------------------------------* *---------------------------------------------------------------------*


08-03-2004


291


BC401

* define client lcl_travel_agency * it will use the interface lif_partners *---------------------------------------------------------------------* INTERFACE lif_partners. METHODS display_partner. EVENTS: partner_created. ENDINTERFACE.

"lif_partners

*---------------------------------------------------------------------* *


*---------------------------------------------------------------------* * CLASS lcl_rental DEFINITION.



METHODS

add_vehicle for event vehicle_created of lcl_vehicle

SAP

METHODS

SAP

importing sender.

Use

Partner

*---------------------------------------------------------------------*

Internal

Only

...

display_attributes.

INTERFACES: lif_partners. PRIVATE SECTION. "-------------------

Use

vehicle_list TYPE TABLE OF REF TO lcl_vehicle. ENDCLASS.


Internal

*---------------------------------------------------------------------* *


Partner

DATA: name TYPE string,

*---------------------------------------------------------------------* *---------------------------------------------------------------------* CLASS lcl_rental IMPLEMENTATION. METHOD lif_partners~display_partner. display_attributes( ). ENDMETHOD. METHOD


constructor.

name = im_name. SET HANDLER add_vehicle FOR ALL INSTANCES.


292


08-03-2004

Only

*

BC401

Lesson: Events

RAISE EVENT lif_partners~partner_created. ENDMETHOD. METHOD

"constructor

add_vehicle.

APPEND sender TO vehicle_list. ENDMETHOD.

METHOD

"add_vehicle

display_attributes.

Internal

Only

DATA: r_vehicle TYPE REF TO lcl_vehicle. skip 2. WRITE: / WRITE:



Partner

r_vehicle->display_attributes( ). ENDLOOP. ENDMETHOD.

"display_attributes

Use

ENDCLASS.


SAP

*

SAP

*---------------------------------------------------------------------* CLASS lcl_travel_agency DEFINITION

*---------------------------------------------------------------------* * *---------------------------------------------------------------------*

Partner

Use

CLASS lcl_travel_agency DEFINITION. PUBLIC SECTION.

Internal

"------------------METHODS:


METHODS

add_partner FOR EVENT partner_created OF lif_partners IMPORTING sender.

Only

METHODS


PRIVATE SECTION. "------------------DATA: name TYPE string, partner_list TYPE TABLE OF REF TO lif_partners. ENDCLASS.

"lcl_travel_agency DEFINITION

*---------------------------------------------------------------------* *


*---------------------------------------------------------------------*


08-03-2004


293


BC401

* *---------------------------------------------------------------------* CLASS lcl_travel_agency IMPLEMENTATION. METHOD display_agency_partners. DATA: r_partner TYPE REF TO lif_partners. WRITE: icon_dependents AS ICON, name. WRITE:

’ Here are the partners of the travel agency: ’.ULINE.ULINE.

LOOP AT partner_list INTO r_partner.

Internal

Only

r_partner->display_partner( ). ENDLOOP. ENDMETHOD. METHOD

"display_agency_partners

constructor.

Partner

name = im_name. SET HANDLER add_partner FOR ALL INSTANCES. ENDMETHOD.

Use

METHOD

"constructor

add_partner.

APPEND sender TO partner_list. "add_partner

*&---------------------------------------------------------------------*

"lcl_travel_agency IMPLEMENTATION

SAPBC401_EVES_B *&

Include

SAPBC401_EVES_B

*

*&---------------------------------------------------------------------* *---------------------------------------------------------------------*

Internal

*


*---------------------------------------------------------------------*

Partner

SAP

SAP

ENDCLASS.

Use

ENDMETHOD.

*

CLASS lcl_carrier DEFINITION. PUBLIC SECTION. "---------------------------------------INTERFACES lif_partners. METHODS: constructor IMPORTING im_name TYPE string, get_name RETURNING value(ex_name) TYPE string, add_airplane FOR EVENT airplane_created OF lcl_airplane IMPORTING sender,


294


08-03-2004

Only

*---------------------------------------------------------------------*

BC401

Lesson: Events

display_airplanes, display_attributes. PRIVATE SECTION. "----------------------------------DATA: name

TYPE string,



*

Internal

Only

*---------------------------------------------------------------------* CLASS lcl_carrier IMPLEMENTATION

*---------------------------------------------------------------------* CLASS lcl_carrier IMPLEMENTATION. METHOD lif_partners~display_partner.

Partner

display_attributes( ). ENDMETHOD.


Use

METHOD add_airplane. APPEND sender TO airplane_list. ENDMETHOD.

"add_airplane

SAP

SAP

METHOD display_attributes. SKIP 2. WRITE: icon_flight AS ICON, name . ULINE. ULINE. display_airplanes( ). "display_attributes

Partner

Use

ENDMETHOD.

METHOD display_airplanes. DATA: r_plane TYPE REF TO lcl_airplane.

Internal

LOOP AT airplane_list INTO r_plane. r_plane->display_attributes( ). ENDLOOP.

Only

ENDMETHOD.

"display_airplanes

METHOD constructor. name = im_name. SET HANDLER add_airplane FOR ALL INSTANCES. RAISE EVENT lif_partners~partner_created. ENDMETHOD.

"constructor

METHOD get_name. ex_name = name.


08-03-2004


295



BC401

"get_name "lcl_carrier IMPLEMENTATION

Use

Partner

Only

Internal

SAP

SAP Only

Internal

Use

Partner

296


08-03-2004

BC401

Lesson: Events

Lesson Summary

Related Information

Use

Partner


Internal

Only

You should now be able to: • Define and trigger events • Handle events • Register and deregister event handling • Explain the key differences between explicit method calls and event-controlled method calls

SAP

SAP Only

Internal

Use

Partner

08-03-2004


297

Unit Summary

BC401

Unit Summary

Only Partner

Use SAP

SAP

Internal

You should now be able to: • Define inheritance relationships between classes • Redefine methods • Create narrowing cast assignments • Create widening cast assignments • Explain the concept of polymorphism with reference to interfaces • Use cast assignments with inheritance to make generic calls • Define and implement interfaces • Implement interface methods • Use interface references to make narrowing cast assignments • Use interface references to make widening cast assignments • Explain the term polymorphism with reference to interfaces • Use cast assignments with interfaces to make generic calls • Define and trigger events • Handle events • Register and deregister event handling • Explain the key differences between explicit method calls and event-controlled method calls

Only

Internal

Use

Partner

298


08-03-2004

BC401

Test Your Knowledge

Partner

What is the ABAP syntax required to redefine an inherited method in a local class?

3.

If you copy a subclass reference to a reference variable that is typed on the superclass (narrowing cast), which components can you access with this reference variable?

SAP

2.

Choose the correct answer(s).

Use

Redefined components of the superclass Newly defined components of the subclass Inherited components of the superclass Redefined components of the subclass

If a reference variable – typed on a superclass – contains a subclass reference and you copy this to a reference variable that is typed on the class (widening cast), which of the following components can you access with this reference variable? Choose the correct answer(s).

□ □ □ □

08-03-2004

A B C D

Redefined components of the superclass Newly defined components of the subclass Inherited components of the superclass Redefined components of the subclass


299

Only

Internal

4.

A B C D

Partner

□ □ □ □

SAP

What is the ABAP syntax required to make a local subclass inherit from a superclass?

Use

1.

Internal

Only

Test Your Knowledge

Test Your Knowledge

BC401

Does an interface have an implementation part?

7.

If you copy an instance reference of a class, which implements an interface, to a reference variable that is typed on the interface (narrowing cast), what components can you access using this reference variable?

Partner

Only

6.


SAP Use

If a reference variable that is typed on an interface contains an instance reference of a class that implements this interface and you copy this to a reference variable that is typed on the class (widening cast), which of the following components can you access with this reference variable? Choose the correct answer(s).

300

□ □

A B

□ □

C D

The components of the interface The components from the class that are not defined on the interface All components of the class The components of the interface for which alias names have been defined


08-03-2004

Only

Internal

The components of the interface The components of the class that are not defined in the interface All components of the class The components of the interface for which alias names have been defined

Partner

8.

A B C D

SAP

□ □ □ □

Use

For what purpose do you use inheritance?

Internal

5.

BC401

Test Your Knowledge

9.

What is the statement for defining events?

Partner

11. With which statement would you define a handler method M_H for event E of class C?

Internal

Only

10. What is the statement for triggering events?

Use

Partner

Internal

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12. With which statement would you register handler method M_H of the reacting instance REF_H with the triggering instance REF_R?

13. Can events be defined in interfaces?

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14. Can events be triggered in interfaces?

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Answers 1.

What is the ABAP syntax required to make a local subclass inherit from a superclass? Answer: Using the INHERITING FROM addition to the CLASS-DEFINITION statement

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2.

What is the ABAP syntax required to redefine an inherited method in a local class?

Refer to the relevant section of the lesson. If you copy a subclass reference to a reference variable that is typed on the superclass (narrowing cast), which components can you access with this reference variable?

SAP

SAP

3.

Answer: A, C Refer to the relevant section of the lesson.

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If a reference variable – typed on a superclass – contains a subclass reference and you copy this to a reference variable that is typed on the class (widening cast), which of the following components can you access with this reference variable? Answer: A, B, C

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Refer to the relevant section of the lesson. For what purpose do you use inheritance? Answer: Inheritance is how generalization/specialization relationships between classes are implemented in a program. Refer to the relevant section of the lesson.

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Answer: Using the REDEFINITION addition to the METHODS statement

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Test Your Knowledge

6.

Does an interface have an implementation part? Answer: No Refer to the relevant section of the lesson. If you copy an instance reference of a class, which implements an interface, to a reference variable that is typed on the interface (narrowing cast), what components can you access using this reference variable? Answer: A Refer to the relevant section of the lesson. If a reference variable that is typed on an interface contains an instance reference of a class that implements this interface and you copy this to a reference variable that is typed on the class (widening cast), which of the following components can you access with this reference variable? Answer: A, B, C, D

SAP

9.

SAP

Refer to the relevant section of the lesson. What is the statement for defining events?

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Answer: EVENTS Refer to the relevant section of the lesson.

Answer: RAISE EVENT Refer to the relevant section of the lesson. 11. With which statement would you define a handler method M_H for event E of class C? Answer: METHODS m_h FOR EVENT e OF c ... . Refer to the relevant section of the lesson.


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10. What is the statement for triggering events?

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Test Your Knowledge

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12. With which statement would you register handler method M_H of the reacting instance REF_H with the triggering instance REF_R? Answer: SET HANDLER ref_h->m_h FOR ref_r. Refer to the relevant section of the lesson.

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Internal

13. Can events be defined in interfaces? Answer: Yes

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Refer to the relevant section of the lesson. 14. Can events be triggered in interfaces?

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Answer: No Refer to the relevant section of the lesson.

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Unit 4 Unit Overview

We will add a few more details (which were deliberately left out earlier) to your understanding of object-oriented programming concepts. These apply equally to local and global classes.

SAP

SAP

The third lesson is about possibilities for generating very specific global classes. In turn, this generation tool uses the Class Builder.

Unit Objectives

Use Internal

Describe the functions of the Class Builder Create global classes using the Class Builder Create interfaces using the Class Builder Reference global classes/interfaces in other Repository objects Create object-oriented transactions (transaction-code-type) Define abstract classes Define abstract methods Define final classes Define final methods Limit the visibility of the constructor Define friend relationships between classes Create persistent objects using the standard technique Load persistent objects using the standard technique Access components of persistent objects


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After completing this unit, you will be able to: • • • • • • • • • • • • • •

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The first lesson will introduce you to the Class Builder, a tool from the ABAP Workbench that you have not used before. You will focus on learning how to apply the techniques that you learned for local classes and interfaces to global classes and interfaces.

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Object-Oriented Repository Objects

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Unit 4: Object-Oriented Repository Objects

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Unit Contents

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Lesson: Global Classes and Interfaces .......................................... 307 Procedure: Importing Local Classes and Interfaces ....................... 315 Procedure: Moving the Method Definition of a Global Class to an Implemented Interface ......................................................... 324 Procedure: Creating an Object-Oriented Transaction ..................... 330 Exercise 18: Global Classes .................................................. 331 Exercise 19: Global Interfaces................................................ 335 Exercise 20: Refactoring Assistant........................................... 347 Lesson: Special Object-Oriented Programming Techniques.................. 352 Exercise 21: Singleton Classes (Optional) .................................. 359 Exercise 22: Friendship Relationships (optional) .......................... 363 Lesson: Persistent Objects in ABAP Objects for SAP Web Application Server 6.20 .................................................................................. 369 Procedure: Creating Persistent Classes .................................... 373

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Lesson: Global Classes and Interfaces

Lesson: Global Classes and Interfaces Lesson Overview This lesson introduces you to a new tool in the ABAP Workbench: The Class Builder, which was integrated into SAP R/3 4.6A at the same time as ABAP Objects. We will examine its main functions and its integration into the ABAP Workbench – especially the Object Navigator.

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Lesson Objectives

SAP

Business Example

Use

Describe the functions of the Class Builder Create global classes using the Class Builder Create interfaces using the Class Builder Reference global classes/interfaces in other Repository objects Create object-oriented transactions (transaction-code-type)

Creating Global Classes and Interfaces

SAP

• • • • •

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Internal

We will demonstrate the use of global standard classes using the powerful example of the SAP Grid Control.

Develop your classes and interfaces as actively integrated Repository objects.

Internal

On the other hand, global classes and global interfaces are individual Repository objects with all of the normal attributes (active integration, versioning, transport system, and so on). The namespace convention (Y*, Z*, or a special customer namespace) reflects the namespace of other Repository objects. Therefore, a special maintenance tool is available in the ABAP Workbench as of SAP R/3 4.6A: the Class Builder.

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In both cases, whether or not the source text is stored separately in include programs is irrelevant.

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As with subroutines, local classes and interfaces can only be used within the program in which they are defined and implemented. The CLASS statement is a local, declarative statement in the program. Just as the TYPES statement defines local data types, the CLASS statement defines local object types.


BC401

SAP Use Internal

Do the same when creating global classes. The global class or global interface is then displayed in the Class Builder table in the editor area of the Object Navigator.

Partner

A dialog box asks you to make further specifications for the new class: Do not change the default specifications at this point. You will learn about the different settings and their effects later.

SAP

As with other Repository objects, the separate navigation area of the Object Navigator makes it the ideal development tool for all Repository objects. It also supports the Class Builder. As with other Repository objects, the easiest way to create a new global class is to use the context menu in the navigation area: First select the package node or select the class node itself within a package.

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Figure 134: Creating Global Classes in the Object Navigator

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Figure 135: Definition of Attributes

SAP

SAP

You can use the input help when you are defining the type attributes. Remember to use meaningful short descriptions.

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Choose the Attributes tab to open the list of all attribute definitions in the class. You can define new attributes here.

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Figure 136: Definition of Methods

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Choose the Methods tab to open the list of all method definitions in the class. You can define new methods here. You can use the input help when defining the attributes. Remember to use meaningful short descriptions. There are separate editor windows for the signature and the implementation.

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Only

Choose the Constructor button to define an instance constructor. The constructor name is chosen automatically and the selection possibilities in the editor window for the signature are restricted appropriately.

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Hint: Methods can be transported separately.

SAP

SAP

If you want to include a local interface in your global class, you must enter the name of the interface in the Interfaces tab. Once you have done that, all of the interface’s components automatically appear under the relevant tabs according to the naming convention and the interface resolution operator.

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Figure 137: Including Global Classes

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In the method list, select a method and choose the Parameter button to go to the signature maintenance. You can define new formal parameters here.

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You can scroll between the signatures using the Previous Method and Next Method buttons. Choose the Methods button to return to the method list.

SAP

You can use the input help when defining the attributes. Remember to use meaningful short descriptions.

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Internal

Figure 138: Definition of Method Signatures

Figure 139: Implementation of Methods

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In the method list, select a method (double-click) or, if a method is already selected, choose the Source code button to go to the signature maintenance. You can implement the modifications here. You can display the method’s signature by choosing the relevant button.

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Figure 140: Displaying the Method Definition

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Choose Goto → Method definition if you want to change the attributes of your method during the implementation.

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Figure 141: Definition of Components Using the Navigation Area

Hint: Print selected portions of the source text using Class → Print or Method → Print.

SAP

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You can also define attributes, methods, or events in the context menu in the Object Navigator’s navigation area. The attributes are then maintained in a dialog box, and not in the table we saw before.

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Figure 142: The Class Builder Testing Environment

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You can test active global classes: The class’s templates are allocated temporarily. Static ones are allocated immediately, instance components are allocated when you choose the Instance button. The system only lists the public components. Methods can be tested using the Call method icon.

1. 2.

Partner

3.

Select an event. Choose the Handler button. This registers a standard method for the event. Call a method in which the event trigger was implemented.

The event that was triggered and all of the exported actual parameters are displayed in a list.

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You can test the triggering of events in a class as follows:

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Importing Local Classes and Interfaces Use The procedure is an easy way to make global copies of local classes and local interfaces.

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In the initial screen of the Class Builder, choose Object type → Import → Local program classes.

3.

Enter the name of the main program and, if the local classes and interfaces were defined within include programs, select Expand Includes.

4.

Choose the button Display Classes/Interfaces.

5.

Enter names for the global classes and interfaces that you want to create. Remember the customer namespace, if applicable.

6.

Select the global classes and interfaces that you want to create and choose the Import button.

SAP

2.

SAP

In the SAP Easy Access Menu, choose Tools → ABAP Workbench → Development → Class Builder or call the transaction SE24.

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1.

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Procedure

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Caution: This function cannot be used from within the Object Navigator.

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Internal

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Internal

Figure 143: Importing a Local Program Class

Other Functions of the Class Builder

SAP

SAP

You set out the inheritance relationships between global classes in the Properties tab.

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Figure 144: Defining an Inheritance Relationship

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Choose the Superclass button to specify an inheritance relationship. In this example, the subclass ZCL_CARGO_PLANE_00 will inherit from superclass ZCL_AIRPLANE_00.

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Internal

Figure 145: Redefining an Inherited Method

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To redefine an inherited method, select the relevant method in the list and choose the Redefine button. Alternatively, you can use the context menu in the navigation area.

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Internal

Figure 146: Defining a Local Type

You can define local types in global classes. This includes local classes in particular.

SAP

All components of the global class have access to these local types, but they are encapsulated to the outside.

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Only

Internal

To edit the implementation parts of these local classes, choose the Impl. button. (Local Class Implementations).

Partner

The same applies for local interfaces in global classes.

SAP

Technically, you are not defining a class within a class, but a class that is local in the Repository object of the global class.

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Internal

Figure 147: Structured Display of Inherited Components

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To improve your understanding of inheritance and interface components, you can set the flag Group by Classes and Interfaces in the User-Specific Settings for the Class Builder. The system will then display the components of the global class in a structure.

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Internal

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Figure 148: Sorting the Component Display of Global Classes

You can also sort all components by five criteria in three levels. To do this, display the appropriate dialog box by choosing the Sort button.

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Inclusion of Global Classes Using the ABAP Editor Like other Repository objects, global classes and interfaces are included in the navigation area of the Object Navigator.

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Internal

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This way, the previously discussed advantages also apply to working with global classes and interfaces.

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Internal

Figure 149: Separating the Navigation and Editing Areas of the Object Navigator.

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SAP Use

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Internal

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Alternatively, you can also choose the Pattern button. The CREATE-OBJECT statement is under ABAP Objects Pattern. You can generate the statement using the input help.

SAP

In the navigation area, select a class name and drag it to the editing area. This creates a CREATE OBJECT statement. You must then add the reference variable and the actual parameters, if applicable, to the statement.

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Internal

Figure 150: Object Instantiation Using Drag&Drop

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The Refactoring Assistant

Internal

Working with the tool is simple, since it is based on Drag&Drop dialogs.

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In an ideal world, all classes, interfaces, and the associations between them would be modeled completely using UML diagrams before developers began implementing them. However, in some cases, the model needs to be adapted during the implementation phase. The Refactoring Assistant offers a range of user-friendly options for you to change Repository objects that you created previously. For example, you can use the Refactoring Assistant to move the components of a class within the inheritance hierarchy. For a complete list of the features in this tool, refer to the SAP Library.

Partner

Use

Alternatively, you can also choose the Pattern button. The CALL-METHOD statement is under ABAP Objects Pattern. You can generate the statement using the input help.

SAP

In the navigation area, select a method name and drag it to the editing area. This creates a CREATE METHOD statement. You must then add the reference variable and the actual parameters, if applicable, to the statement.

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Internal

Figure 151: Method Calls Using Drag&Drop

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Internal

Figure 152: Working with the Refactoring Assistant

SAP Use

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Internal

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Generally, you do not adjust the implementation of methods, since you cannot know how much you will need to alter object references after making these changes.

SAP

Hint: The Tool Info button opens the SAP Library article about the Refactoring Assistant. There you can also find the descriptions of the tool’s other abilities.

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Change to editing mode and choose a global class that implements a global interface.

2.

Choose the Refactoring Assistant from the Utilities menu.

3.

In the tree structure that appears, open the folder for the method you want to move and for the “target” – in this case, the implemented interface.

4.

Move the method to the interface.

5.

Save your work. Caution: You might also need to, adapt statements calling the method in the source code.

7.

Activate both the class and the interface.

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Only

Internal

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The SAP Control Framework is a collection of global classes and interfaces that you can use to include SAP GUI controls in your ABAP Objects programs, regardless of the platform. We will show you how to use SAP standard classes effectively. We will demonstrate this with the widely used SAP Grid Control.

SAP

Use of SAP Standard Classes – Application Example

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1.

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Moving the Method Definition of a Global Class to an Implemented Interface

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Internal

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SAP Grid Control contains a number of interactive standard functions that users of lists often need for example, print, export, and so on). As a developer, you have the option of hiding these standard functions. When required, you can also adapt the implementations to fit the needs of your application. You can also add your own functions to the application toolbar.

SAP

SAP Grid Control is a tool with which you can display non-hierarchical lists in a standardized form. The list data is displayed in tables. It is very easy to work with as only very few programming steps have to be carried out.

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Internal

Figure 153: SAP Grid Control

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Let us take a common case as an example: Placing an SAP Grid Control in a screen area with a fixed size. You need to create an instance of each of the global classes CL_GUI_CUSTOM_CONTAINER and CL_GUI_ALV_GRID.

Partner

There are different types of container controls. However, they all encapsulate fundamental control functions, such as scroll bars.

SAP

The technical connection between screen control and application control is implemented using container controls. Generally, application controls (SAP Grid Control, tree control, picture control) always have to be embedded in a container control. In turn, the container control must be connected to the screen.

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Figure 154: Including an SAP Grid Control Instance in a Dialog Program

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For normal display, the follow programming steps are sufficient:

SAP

2.

Use

If this table has a global row type, you can transfer the name of this global structure to the same method. Then the Grid Control instance automatically creates the field catalog.

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4.

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3.

Use the fullscreen editor of the Screen Painter to define a custom control area on your screen. Create an instance of the class CL_GUI_CUSTOM_CONTAINER and transfer the name of the custom control area to the constructor. Create an instance of the class CL_GUI_GUI_ALV_GRID and transfer the reference to the custom control instance to the constructor. Call the method SET_TABLE_FOR_FIRST_DISPLAY of the grid control instance and transfer the internal standard table to it.

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Figure 155: Displaying Application Data Using an SAP Grid Control Instance


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If you change the contents of the internal tables at runtime, you only need to call the method REFRESH_TABLE_DISPLAY in the relevant dialog step to refresh the display. Note: Extensive documentation about the SAP Control Framework is available. The SAP Library contains comprehensive descriptions of all classes and a complete tutorial.

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Individual elements of the SAP Control Framework are also covered in other courses.

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OO Transactions as a Transaction Type

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Internal

SAP

In transaction maintenance, you can create a transaction code as an OO transaction. This means that you link the transaction code either to the transaction service of the ABAP Objects services for persistent objects or to a public method in a global or local class of a program. When calling this type of OO transaction, which is linked to an instance method, the system automatically creates an instance of the class in its own internal session and then executes this instance method.

Use

SAP also offers a separate comprehensive course about dialog programming with the EnjoySAP controls. It covers all aspects, including complex programming techniques like Drag&Drop functions.

Internal

The Object Navigator also contains the Enjoy Demo Center, which makes it very easy to use standard template programs. You can find it under Environment → Examples → Control Examples.

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•

The constructor cannot contain any IMPORTING parameters

•

ABAP list displays cannot be processed

Only

SAP Internal

Caution: Global classes in ABAP Objects cannot contain screen definitions. Thus, when you create a link to a global class, note the following:

Therefore, you may have to resort to methods in local program classes. Naturally, you can then use all the conventional dialog programming techniques.

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Use

Thus, users now have the opportunity to call methods themselves in the usual way (through menu options, command field entries, and so on).

SAP

If the OO Transaction Model flag is set, the transaction code is linked to the transaction service of the ABAP Objects services. Conversely, if it is not set, you can call any method in a global or local class.

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Internal

Figure 156: Creating an OO Transaction Code

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Call the usual dialog for creating a transaction code and enter a short text.

2.

Choose the option Method of a Class (OO Transaction) as an Initial Object.

3.

Leave the OO Transaction Model flag unchecked if you want to link the transaction code to a normal instance method.

4.

Enter the Class Name and Method. Set the Local in Program flag and enter the program name, if you are using a local class.

5.

Save the transaction code.

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Creating an Object-Oriented Transaction

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Exercise 18: Global Classes Exercise Objectives After completing this exercise, you will be able to: • Describe the functions of the Class Builder • Create global classes using the Class Builder

Only

Internal

Business Example Create a global class to represent hotels.

Create a global class for hotels. Create the global class ZCL_##_HOTEL. (Where ## is your two-digit group number).

2.

Define the following attributes in the class:

Use

of type STRING

as a private instance attribute

MAX_BEDS

of type I


N_O_HOTELS

of type I

as a private static attribute

Partner

NAME

SAP

SAP

1.

Define the following methods in the class: CONSTRUCTOR

Instance constructor for setting the private attributes with the import parameters IM_NAME and IM_BEDS

DISPLAY_ATTRIBUTES

Instance method for displaying attributes in an ABAP list

DISPLAY_N_O_HOTELS

Static method to display the number of created hotel instances in an ABAP list


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Maintain the short texts. 3.

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Task 1:


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Maintain the short texts.

Task 2: Check your work. 1.

Activate your class.

2.

Test your class in the Class Builder’s testing environment.

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Solution 18: Global Classes Task 1: Create a global class for hotels. 1.

Create the global class ZCL_##_HOTEL. (Where ## is your two-digit group number).

Only

Follow the processes as outlined in the relevant section of this lesson. Model solution: CL_HOTEL

Define the following attributes in the class: NAME

of type STRING


MAX_BEDS

of type I


N_O_HOTELS

of type I

as a private static attribute

SAP

SAP

2.

Use

Partner

Caution: If you copy from this model solution, you must remove the inheritance relationship to the global class CL_HOUSE and the global interface IF_PARTNERS.

Define the following methods in the class: CONSTRUCTOR

Instance constructor for setting the private attributes with the import parameters IM_NAME and IM_BEDS

DISPLAY_ATTRIBUTES

Instance method for displaying attributes in an ABAP list

DISPLAY_N_O_HOTELS

Static method to display the number of created hotel instances in an ABAP list

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3.

Follow the processes as outlined in the relevant section of this lesson. Speak to your instructor if you have any questions.

Partner

Maintain the short texts. a) b)

Internal

a) b)


BC401

Maintain the short texts. a) b)


Task 2: Check your work. Activate your class. a) 2.

Test your class in the Class Builder’s testing environment. a) b)


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Exercise 19: Global Interfaces Exercise Objectives

Business Example

Task 1: 1.

If applicable, change the interface name in your UML diagram to ZIF_##_PARTNERS. (Where ## is your two-digit group number).

2.

Create the global interface ZIF_##_PARTNERS.

SAP

SAP

Create a global interface for generalized access to business partner instances.

Use

Task 2: Have your hotel class implement the interface. 1.

If necessary, add the class ZCL_##_HOTEL to your UML diagram. It should implement the DISPLAY_PARTNER interface method and trigger the instance event PARTNER_CREATED. Draw the corresponding relationships in your diagram.

2.

Include the interface in your hotel class. Continued on next page


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Hint: Import the local interface from your program ZBC401_##_MAIN or from the previous lesson’s sample solution SAPBC401_EVES_MAIN_B.

Partner

Define the instance method DISPLAY_PARTNER and the instance event PARTNER_CREATED in the interface.

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Use

Partner

Add a hotel as a new business partner in your program for managing a travel agency’s business partners. Replace the local interface that you have been using with a global one, so that it can also be implemented by the global hotel class.

Internal

Only

After completing this exercise, you will be able to: • Describe the functions of the Class Builder • Create interfaces using the Class Builder • Reference global classes/interfaces in other Repository objects


BC401

3.

Implement the interface method in such a way that the hotel’s DISPLAY_ATTRIBUTES instance method is called.

4.

Trigger the instance event in a suitable instance method of the hotel class.

Task 3: Complete your program ZBC401_##_MAIN program or copy the program SAPBC401_EVES_MAIN_B (where ## is your two-digit group number).

2.

Remove the definition of the local interface and adapt all places where it was used to suit the new global interface.

3.

Define a reference variable, specify your global hotel class as the type, and create an instance.

4.

Run your program. If you have done everything correctly, the simple instantiation should be enough to be able to display the hotel attributes on the list as well.

Use

Partner

1.

Internal

Only

Add an instance of your global hotel class to your main program.

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SAP Only

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Solution 19: Global Interfaces Task 1: Create a global interface for generalized access to business partner instances. 1.

If applicable, change the interface name in your UML diagram to ZIF_##_PARTNERS. (Where ## is your two-digit group number).

2.


Create the global interface ZIF_##_PARTNERS.

Hint: Import the local interface from your program ZBC401_##_MAIN or from the previous lesson’s sample solution SAPBC401_EVES_MAIN_B.

SAP

Follow the processes as outlined in the relevant section of this lesson. Speak to your instructor if you have any questions. Model solution: IF_PARTNERS

Task 2:

Use

If necessary, add the class ZCL_##_HOTEL to your UML diagram. It should implement the DISPLAY_PARTNER interface method and trigger the instance event PARTNER_CREATED. Draw the corresponding relationships in your diagram. a)

2.

Include the interface in your hotel class. a) b)

3.



Implement the interface method in such a way that the hotel’s DISPLAY_ATTRIBUTES instance method is called. a) b)

Follow the processes as outlined in the relevant section of this lesson. Speak to your instructor if you have any questions. Continued on next page

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1.

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Have your hotel class implement the interface.

SAP

a) b) c)

Use

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Define the instance method DISPLAY_PARTNER and the instance event PARTNER_CREATED in the interface.

Internal

Only

a)


4.

BC401

Trigger the instance event in a suitable instance method of the hotel class. a)


Task 3: Add an instance of your global hotel class to your main program. Complete your program ZBC401_##_MAIN program or copy the program SAPBC401_EVES_MAIN_B (where ## is your two-digit group number). a)

2.

Remove the definition of the local interface and adapt all places where it was used to suit the new global interface. a)

Define a reference variable, specify your global hotel class as the type, and create an instance. a)

Run your program. If you have done everything correctly, the simple instantiation should be enough to be able to display the hotel attributes on the list as well. a)


Internal


Only

SAPBC401_CLSS_MAIN_A REPORT

sapbc401_clss_main_a.


TYPE-POOLS icon.


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4.


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SAP

3.


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b)

Carry out this step in the usual manner. Additional information is available in the SAP Library. Model solution: SAPBC401_CLSS_MAIN_A

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1.

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INCLUDE sapbc401_vehd_j. INCLUDE sapbc401_clss_a. DATA: r_vehicle TYPE REF TO lcl_vehicle, r_truck TYPE REF TO lcl_truck, r_bus


r_passenger TYPE REF TO lcl_passenger_plane, r_cargo TYPE REF TO lcl_cargo_plane,

Internal

Only

r_carrier TYPE REF TO lcl_carrier, r_rental TYPE REF TO lcl_rental, r_agency TYPE REF TO lcl_travel_agency,

Partner

r_hotel TYPE REF TO cl_hotel.


Use

******* create travel_agency *****************************************

SAP

SAP

CREATE OBJECT r_agency EXPORTING im_name = ’Fly&Smile Travel’.

******* create rental ***************************************** CREATE OBJECT r_rental EXPORTING im_name = ’HAPPY CAR RENTAL’. ******* create truck *****************************************

Partner

Use

CREATE OBJECT r_truck EXPORTING im_make = ’MAN’ im_cargo = 45. ******* create truck ***************************************** CREATE OBJECT r_bus EXPORTING im_make = ’Mercedes’

Internal

im_passengers = 80.

******* create truck *****************************************

Only

CREATE OBJECT r_truck EXPORTING im_make = ’VOLVO’ im_cargo = 48. ***** Create CARRIER ******************************************** CREATE OBJECT r_carrier EXPORTING im_name = ’Smile&Fly Travel’. ***** Passenger Plane ******************************************** CREATE OBJECT r_passenger EXPORTING im_name = ’LH BERLIN’ im_planetype = ’747-400’


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im_seats = 345. ***** cargo Plane ************************************************ CREATE OBJECT r_cargo EXPORTING im_name = ’US Hercules’ im_planetype = ’747-500’ im_cargo = 533.

******* create hotel *****************************************

Internal

Only

CREATE OBJECT r_hotel EXPORTING im_name = ’Holiday Inn’ im_beds = 345.

******* show attributes of all partners of travel_agency ******

SAPBC401_VEHD_J *&---------------------------------------------------------------------* *&

Include

SAPBC401_VEHD_J

*

*&---------------------------------------------------------------------* *---------------------------------------------------------------------*

Use

Partner


*---------------------------------------------------------------------* *---------------------------------------------------------------------* *

CLASS lcl_vehicle DEFINITION

SAP

SAP

* work with the global interface if_hotel

*---------------------------------------------------------------------*

Use

*---------------------------------------------------------------------* *

CLASS lcl_truck DEFINITION

*---------------------------------------------------------------------*

Internal

* *---------------------------------------------------------------------*

Partner

...

...

*

CLASS lcl_bus DEFINITION

*---------------------------------------------------------------------* * *---------------------------------------------------------------------* ... *---------------------------------------------------------------------* *


*---------------------------------------------------------------------* *


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*---------------------------------------------------------------------*

BC401


*---------------------------------------------------------------------* CLASS lcl_rental DEFINITION. PUBLIC SECTION. "------------------METHODS:


METHODS

add_vehicle FOR EVENT vehicle_created OF lcl_vehicle

METHODS

display_attributes.

INTERFACES:

if_partners.

Internal

Only

IMPORTING sender.

PRIVATE SECTION. "------------------DATA: name TYPE string,

Partner

vehicle_list TYPE TABLE OF REF TO lcl_vehicle. ENDCLASS.


*

Use

*---------------------------------------------------------------------* CLASS lcl_rental IMPLEMENTATION

*---------------------------------------------------------------------* *

SAP

SAP

*---------------------------------------------------------------------* CLASS lcl_rental IMPLEMENTATION. METHOD if_partners~display_partner. display_attributes( ).

METHOD


Partner

Use

ENDMETHOD. constructor.

name = im_name. SET HANDLER add_vehicle FOR ALL INSTANCES.

METHOD

"constructor

Only

Internal

RAISE EVENT if_partners~partner_created. ENDMETHOD. add_vehicle.

APPEND sender TO vehicle_list. ENDMETHOD. METHOD

"add_vehicle

display_attributes.

DATA: r_vehicle TYPE REF TO lcl_vehicle. skip 2. WRITE: / WRITE:




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r_vehicle->display_attributes( ). ENDLOOP. ENDMETHOD.

"display_attributes

ENDCLASS.


*---------------------------------------------------------------------* CLASS lcl_travel_agency DEFINITION

*---------------------------------------------------------------------* * *---------------------------------------------------------------------*

Partner

CLASS lcl_travel_agency DEFINITION. PUBLIC SECTION. "------------------constructor IMPORTING im_name TYPE string.

METHODS

add_partner FOR EVENT partner_created OF if_partners

Use

METHODS:

IMPORTING sender. METHODS


SAP

SAP

PRIVATE SECTION. "------------------DATA: name TYPE string, partner_list TYPE TABLE OF REF TO if_partners. "lcl_travel_agency DEFINITION

*---------------------------------------------------------------------* *


*---------------------------------------------------------------------*

Internal

* *---------------------------------------------------------------------*

Partner

Use

ENDCLASS.

Internal

Only

*

CLASS lcl_travel_agency IMPLEMENTATION. DATA: r_partner TYPE REF TO if_partners. WRITE: icon_dependents AS ICON, name. WRITE:

’ Here are the partners of the travel agency: ’.ULINE.ULINE.

LOOP AT partner_list INTO r_partner. r_partner->display_partner( ). ENDLOOP. ENDMETHOD. METHOD

"display_agency_partners

constructor.


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METHOD display_agency_partners.

BC401


name = im_name. SET HANDLER add_partner FOR ALL INSTANCES. ENDMETHOD.

METHOD

"constructor

add_partner.

APPEND sender TO partner_list. ENDMETHOD.

"add_partner "lcl_travel_agency IMPLEMENTATION

Internal

Only

ENDCLASS.

SAPBC401_CLSS_A *------------------------------------------------------------------*

Partner

*

INCLUDE SAPBC401_CLSS_A

*------------------------------------------------------------------* * work with interface if_partners

Use

* implement and raise events in lcl_carrier *------------------------------------------------------------------* *


*

*------------------------------------------------------------------*

SAP

SAP

... *---------------------------------------------------------------------* *


*---------------------------------------------------------------------* ...

Partner

Use

*---------------------------------------------------------------------* *


*---------------------------------------------------------------------* *

Internal

*---------------------------------------------------------------------* ... *---------------------------------------------------------------------* CLASS lcl_carrier DEFINITION

Only

*

*---------------------------------------------------------------------* * *---------------------------------------------------------------------* CLASS lcl_carrier DEFINITION. PUBLIC SECTION. "---------------------------------------INTERFACES if_partners. METHODS: constructor IMPORTING im_name TYPE string,


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get_name RETURNING value(ex_name) TYPE string, add_airplane FOR EVENT airplane_created OF lcl_airplane IMPORTING sender, display_airplanes, display_attributes. PRIVATE SECTION. "----------------------------------DATA: name

TYPE string,

ENDCLASS.


*---------------------------------------------------------------------* *


Partner

*---------------------------------------------------------------------* CLASS lcl_carrier IMPLEMENTATION. METHOD if_partners~display_partner. ENDMETHOD.

Use

display_attributes( ). "lif_partners~display_partner

METHOD add_airplane.

SAP

SAP

APPEND sender TO airplane_list. ENDMETHOD.

Internal

Only

airplane_list TYPE TABLE OF REF TO lcl_airplane.

"add_airplane

METHOD display_attributes. SKIP 2.

Partner

Use

WRITE: icon_flight AS ICON, name . ULINE. ULINE. display_airplanes( ).

Internal

ENDMETHOD.

"display_attributes

METHOD display_airplanes. DATA: r_plane TYPE REF TO lcl_airplane.

Only

LOOP AT airplane_list INTO r_plane. r_plane->display_attributes( ). ENDLOOP. ENDMETHOD.

"display_airplanes

METHOD constructor. name = im_name. SET HANDLER add_airplane FOR ALL INSTANCES. RAISE EVENT if_partners~partner_created. ENDMETHOD.

"constructor


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METHOD get_name. ex_name = name. ENDMETHOD. ENDCLASS.

"get_name "lcl_carrier IMPLEMENTATION

Use

Partner

Only

Internal

SAP

SAP Only

Internal

Use

Partner

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BC401

Use

Partner

Only

Internal

SAP

SAP Only

Internal

Use

Partner

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Exercise 20: Refactoring Assistant Exercise Objectives After completing this exercise, you will be able to: • Describe the functions of the Class Builder • Create global classes using the Class Builder

Only

Include your global hotel class in a class hierarchy.

Define a global superclass for houses and have your hotel class inherit from it. 1.

If necessary, add the class ZCL_##_HOUSE to your UML diagram. (Where ## is your two-digit group number).

SAP

Create the global class ZCL_##_HOTEL and leave it empty.

3.

Define an inheritance relationship to make ZCL_##_HOUSE the superclass and ZCL_##_HOTEL the subclass.

Use

Task 2: 1.

Use the Refactoring Assistant to move the NAME attribute, the instance constructor, and the DISPLAY_ATTRIBUTES method into the class ZCL_##_HOUSE.

2.

Adapt the signature and the implementation of the instance constructor in the superclass.

3.

Adapt the implementation of the DISPLAY_ATTRIBUTES method in the superclass.

4.

Overload the instance constructor in the subclass.

5.

Redefine the DISPLAY_ATTRIBUTES method in the subclass. Continued on next page

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Only

Internal

Move the general components of the ZCL_##_HOTEL class to the superclass.

Partner

2.

SAP

It will define the attribute NAME and the method DISPLAY_ATTRIBUTES. The class ZCL_##_HOTEL will inherit from it. Draw the relationships in your diagram.

Use

Partner

Task 1:

Internal

Business Example


6.

BC401

Observe the execution of the program in the ABAP Debugger. If you have done everything correctly, the display of the list should be the same as in the previous exercise.

Use

Partner

Only

Internal

SAP

SAP Only

Internal

Use

Partner

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Solution 20: Refactoring Assistant Task 1: Define a global superclass for houses and have your hotel class inherit from it. 1.

If necessary, add the class ZCL_##_HOUSE to your UML diagram. (Where ## is your two-digit group number).

Only

a)

Create the global class ZCL_##_HOTEL and leave it empty. a) b) c)

3.

Define an inheritance relationship to make ZCL_##_HOUSE the superclass and ZCL_##_HOTEL the subclass. Follow the processes as outlined in the relevant section of this lesson. Speak to your instructor if you have any questions.

Task 2:

Use

Use the Refactoring Assistant to move the NAME attribute, the instance constructor, and the DISPLAY_ATTRIBUTES method into the class ZCL_##_HOUSE. a) b)

2.


Adapt the signature and the implementation of the instance constructor in the superclass. a) b)



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Only

Internal

1.

Partner

Move the general components of the ZCL_##_HOTEL class to the superclass.

SAP

a) b)

SAP

Follow the processes as outlined in the relevant section of this lesson. Speak to your instructor if you have any questions. Model solution: CL_HOUSE

Use

Partner

2.


Internal

It will define the attribute NAME and the method DISPLAY_ATTRIBUTES. The class ZCL_##_HOTEL will inherit from it. Draw the relationships in your diagram.


3.

Adapt the implementation of the DISPLAY_ATTRIBUTES method in the superclass. a) b)

4.

Only


Observe the execution of the program in the ABAP Debugger. If you have done everything correctly, the display of the list should be the same as in the previous exercise. Carry out this step in the usual manner. Additional information is available in the SAP Library.

Use

a)

Internal

Partner


Redefine the DISPLAY_ATTRIBUTES method in the subclass. a) b)

6.


Overload the instance constructor in the subclass. a) b)

5.

BC401

SAP

SAP Only

Internal

Use

Partner

350


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Lesson Summary

Only

Internal

You should now be able to: • Describe the functions of the Class Builder • Create global classes using the Class Builder • Create interfaces using the Class Builder • Reference global classes/interfaces in other Repository objects • Create object-oriented transactions (transaction-code-type)

Related Information

Use

Partner

... about this topic is available in the SAP Library.

SAP

SAP Only

Internal

Use

Partner

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Lesson: Special Object-Oriented Programming Techniques Lesson Overview

Internal

Only

In this lesson, you will complete your knowledge of object-oriented programming. The concepts introduced here apply to other object-oriented programming languages in the same or in a similar way. They can be used freely in ABAP Objects, both with local and global classes.


Partner SAP

In such an abstract class, you can define abstract methods (amongst other things) – that is, you can leave their implementation open. If the subclass of that class is not abstract, the abstract methods must must be redefined there. That is, it must be implemented for the first time. Note: The relevant flag is in the Class Builder, in the Properties tab for that class or method.

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Only

Internal

You can prevent the instantiation of a class by using the ABSTRACT addition with the CLASS statement. Superclasses are a typical use for abstract classes, as they are not intended to be instantiated themselves, but their subclasses are.

Partner

Abstract Classes and Abstract Methods

You want to add special object-oriented programming techniques to your ABAP Objects implementations.

SAP

Business Example

Use

Define abstract classes Define abstract methods Define final classes Define final methods Limit the visibility of the constructor Define friend relationships between classes

Use

• • • • • •

Lesson: Special Object-Oriented Programming Techniques

Internal

Figure 157: Abstract Classes and Abstract Methods

References to such abstract classes can therefore be used for polymorphic access to subclass instances.

SAP

Only

Internal

Note: You will find the relevant flag in the Class Builder, under the Properties tab for that class or method.

Partner

You can prevent a method from being redefined by using the FINAL addition with the METHODS statement.

You can prevent a class from being inherited by using the FINAL addition with the CLASS statement.

SAP

Final Classes and Methods

Use

Static methods cannot be abstract because they cannot be redefined.

Use

Partner

Only

BC401

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353

BC401

Internal

Figure 158: Final Classes and Methods

Thus, all methods of a final class are implicitly final. Therefore, you may not repeat the FINAL addition in the methods themselves.

Visibility of the Instance Constructor

Only

Internal

Note: The relevant flag is in the Class Builder, in the Properties tab for the relevant class.

Partner

Use

You can limit the instantiability of a class by using the CREATE addition with the CLASS statement.

SAP

SAP

Classes that are abstract and final should only contain static components.

Use

Partner

Only


354


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SAP Use Internal

In some cases, classes have to work together so closely that one or both classes need access to the other’s protected and private components. Similarly, they need to be able to create instances of these other classes regardless of the visibility of the constructors. To avoid making these options available to all users, you can use the concept of class friendship. A class can provide friendship to other classes and interfaces (and hence all classes that implement the interface). This is the purpose of the FRIENDS addition of the CLASS statement and the Friends tab in the Class Builder. There, all classes and interfaces that grant friendship are listed.

08-03-2004


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Only

Friendship

Partner

Note: Regardless of that, the instance constructor must always be defined syntactically in the public section.

SAP

The variant CLASS ... DEFINITION CREATE PUBLIC ... is the standard case, that is the normal definition of a class. The other two variants limit the context in which the CREATE OBJECT statement can appear, as specified above. In that sense, they can determine the visibility section for the instance constructor.

Use

Partner

Only

Internal

Figure 159: Implicit Setting of the Instance Constructor’s Visibility


BC401

In principle, granting friendship is one-sided: A class granting friendship is not automatically a friend of its friends. If a class granting friendship wants to access the non-public components of a friend, this friend must also explicitly grant friendship to it.

Use

Partner

Only

Internal

Use

Only

Internal

Conversely, granting friendship is not inherited. A friend of a superclass is therefore not automatically a friend of its subclasses.

Partner

The friend property is inherited: Classes that inherit from friends and interfaces containing a friend (as a component interface) also become friends. Therefore, extreme caution is advised when granting friendship. The higher up a friend is in the inheritance tree, the more subclasses can access all components of a class that grants friendship.

SAP

SAP

Figure 160: Definition of Friendship Relationships

356


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Internal

Figure 161: Areas of Use for Friendship Relationships

SAP

Classes Without Multiple Instantiation

Use

Only

Internal

Partner

There are many cases in which you need to prevent a class from being instantiated more than once per program context. This can be done using the aforementioned singleton concept:

SAP

A typical application of the friend relationship between classes is when methods that access the same data are distributed over several classes. This common data is, however, to be protected from access by “foreign” classes. In such friendships, you can make the class containing the data a singleton - that is, make sure it can only be instantiated once in each program instance.

Use

Partner

Only

BC401

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BC401

Use

Partner

Only

Internal

Figure 162: Singleton Classes

SAP

A public static component could then make the reference to the class available to an external user.

SAP

The class is defined with the additions FINAL and CREATE PRIVATE and is instantiated using its static constructor.

Only

Internal

Use

Partner

358


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BC401


Exercise 21: Singleton Classes (Optional) Exercise Objectives

Only

Business Example

Task 1:

Use

2.

Define the attribute R_SINGLETON for a reference to the singleton instance, making sure that the attribute has a suitable type.

3.

Define and implement the method GET_SINGLETON. It will provide the reference to the singleton instance.

4.

Ensure that the singleton instance is only created with the first call of the GET_SINGLETON method.

Task 2: Create a singleton instance.

08-03-2004

1.

Create the executable program ZBC401_##_MAIN_SPECIAL. (Where ## is your two-digit group number).

2.

Define a reference variable for the singleton instance.

3.

Create the singleton instance.


359

Only

Internal

Create the global class ZCL_##_SINGLETON. (Where ## is your two-digit group number). When doing so, specify the necessary attributes for the singleton class.

Partner

1.

SAP

SAP

Create a singleton class.

Use

Partner

You need a class that can be instantiated no more than once per program context.

Internal

After completing this exercise, you will be able to: • Describe the functions of the Class Builder • Create global classes using the Class Builder • Define singleton classes • Instantiate singleton classes


BC401

Solution 21: Singleton Classes (Optional) Task 1: Create a singleton class. Create the global class ZCL_##_SINGLETON. (Where ## is your two-digit group number). When doing so, specify the necessary attributes for the singleton class. a) b)

Define the attribute R_SINGLETON for a reference to the singleton instance, making sure that the attribute has a suitable type. a)

3.

Define and implement the method GET_SINGLETON. It will provide the reference to the singleton instance.

SAP

Ensure that the singleton instance is only created with the first call of the GET_SINGLETON method. a)

Use the relevant sections of the lesson as a guide.

Task 2: Create a singleton instance. Create the executable program ZBC401_##_MAIN_SPECIAL. (Where ## is your two-digit group number). a) b) 2.

Carry out this step in the usual manner. Additional information is available in the SAP Library. Model solution: SAPBC401_SPCS_MAIN_A

Define a reference variable for the singleton instance. a)



360


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Only

Internal

1.

Partner

Use


SAP

a) 4.


Use

Partner

2.

Carry out this step in the usual manner. Additional information is available in the SAP Library. Specify the attributes as they are outlined in the relevant section of this lesson.

Internal

Only

1.

BC401


3.

Create the singleton instance. a)



Internal

Only

SAPBC401_SPCS_MAIN_A REPORT sapbc401_spcs_main_a.

Partner

DATA: r_single TYPE REF TO cl_singleton.


Use

r_single = cl_singleton=>get_singleton( ).

SAP

SAP Only

Internal

Use

Partner

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BC401

Use

Partner

Only

Internal

SAP

SAP Only

Internal

Use

Partner

362


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BC401


Exercise 22: Friendship Relationships (optional) Exercise Objectives

Only Partner

Business Example Create a global class for travel agents that can access the private attributes of a singleton class that is a friend. The class must buffer flight connection data.

Use

Task 1: Buffer the flight data in a singleton class.

SAP

Hint: You can use the global table kind TY_CONNECTIONS. Make sure that this internal table is filled with data from the transparent table SPFLI, but only when the singleton instance is accessed for the first time.

Task 2: Create a global class for travel agencies and have the singleton class grant it friendship. Enable the new global class to pass flight connection data to a user. 1.

Create the global class ZCL_##_AGENCY. (Where ## is your two-digit group number). Have the singleton class grant it friendship.

2.

Define the private instance attribute NAME of type STRING. Continued on next page

08-03-2004


363

Only

Internal

2.

Partner

Use

Add the attribute CONNECTION_LIST for the flight connection data to your ZCL_##_SINGLETON singleton class, making sure that the right attributes have been set for the flight connection data. (Where ## is your two-digit group number).

SAP

1.

Internal

After completing this exercise, you will be able to: • Describe the functions of the Class Builder • Create global classes using the Class Builder • Define friendship relationships • Access private attributes of a friendship-granting class

BC401

3.

Define and implement an instance constructor that sets the private attribute NAME.

4.

Define the public instance method GET_CONNECTION with the following signature: Kind

Reference type

IM_CARRID

Importing

S_CARR_ID

IM_CONNID

Importing

S_CONN_ID

EX_CONNECTION

Exporting

SPFLI

Implement your method in such a way that the additional data for selected flight connections can be read and exported from the private internal table of the singleton instance using single-record access. If the required data record does not exist, it is enough if you display a message in the ABAP list.

SAP

Task 3:

Use Internal

Add a reference variable for a travel agency instance to the executable program ZBC401_##_MAIN_SPECIAL that you created earlier. (Where ## is your two-digit group number).

2.

Create a travel agency instance.

3.

Call the GET_CONNECTION method for an existing flight connection from the flight data model (for example, LH/0400) and display the data in the ABAP list.


08-03-2004

Only

364

1.

Partner

Create a travel agency instance and have it provide the data of a flight connection.

SAP

Hint: If required, use the statement CLASS ... DEFINITION LOAD to syntactically enable direct access to the static components of the class.

Use

Partner

5.

Name

Internal

Only


BC401


Solution 22: Friendship Relationships (optional) Task 1: Buffer the flight data in a singleton class. Add the attribute CONNECTION_LIST for the flight connection data to your ZCL_##_SINGLETON singleton class, making sure that the right attributes have been set for the flight connection data. (Where ## is your two-digit group number).

a) b) 2.

Make sure that this internal table is filled with data from the transparent table SPFLI, but only when the singleton instance is accessed for the first time.

SAP

a)

SAP

Speak to your instructor if you have any questions. Model solution: CL_SINGLETON


Task 2:

Use

a) b) 2.

Define the private instance attribute NAME of type STRING. a)

3.

Carry out this step in the usual manner. Additional information is available in the SAP Library. Model solution: CL_AGENCY


Define and implement an instance constructor that sets the private attribute NAME. a)

Carry out this step in the usual manner. Additional information is available in the SAP Library. Continued on next page

08-03-2004


365

Only

Internal

Create the global class ZCL_##_AGENCY. (Where ## is your two-digit group number). Have the singleton class grant it friendship.

Partner

Create a global class for travel agencies and have the singleton class grant it friendship. Enable the new global class to pass flight connection data to a user. 1.

Use

Partner

Hint: You can use the global table kind TY_CONNECTIONS.

Internal

Only

1.


Define the public instance method GET_CONNECTION with the following signature: Name

Kind

Reference type

IM_CARRID

Importing

S_CARR_ID

IM_CONNID

Importing

S_CONN_ID

EX_CONNECTION

Exporting

SPFLI

a)

Implement your method in such a way that the additional data for selected flight connections can be read and exported from the private internal table of the singleton instance using single-record access. If the required data record does not exist, it is enough if you display a message in the ABAP list.

SAP Use

Create a travel agency instance and have it provide the data of a flight connection. Add a reference variable for a travel agency instance to the executable program ZBC401_##_MAIN_SPECIAL that you created earlier. (Where ## is your two-digit group number). a) 2.


Create a travel agency instance. a)



366


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Only

1.


Partner

Task 3:

Internal

a)

SAP

Hint: If required, use the statement CLASS ... DEFINITION LOAD to syntactically enable direct access to the static components of the class.

Use

Partner

5.


Internal

Only

4.

BC401

BC401


3.

Call the GET_CONNECTION method for an existing flight connection from the flight data model (for example, LH/0400) and display the data in the ABAP list. a)


Result

Internal

Only


SAPBC401_SPCS_MAIN_B REPORT

sapbc401_spcs_main_b.

Partner

DATA: r_single TYPE REF TO cl_singleton, r_agency TYPE REF TO cl_agency, rec TYPE spfli.

Use

START-OF-SELECTION.

SAP Use

r_agency->get_connection( EXPORTING im_carrid = ’LH’

WRITE: / rec-carrid, rec-connid, rec-cityfrom, rec-cityto.

SAP

r_single = cl_singleton=>get_singleton( ).

Internal

*########################

CREATE OBJECT r_agency EXPORTING im_name = ’Agency’.

Partner

im_connid = ’0400’ IMPORTING ex_connection = rec ).

Only

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Lesson Summary

Only

Related Information

Use

Partner


Internal

You should now be able to: • Define abstract classes • Define abstract methods • Define final classes • Define final methods • Limit the visibility of the constructor • Define friend relationships between classes

SAP

SAP Only

Internal

Use

Partner

368


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BC401

Lesson: Persistent Objects in ABAP Objects for SAP Web Application Server 6.20

Lesson: Persistent Objects in ABAP Objects for SAP Web Application Server 6.20 Lesson Overview

Only

Lesson Objectives • • •

Create persistent objects using the standard technique Load persistent objects using the standard technique Access components of persistent objects

Use

Partner


SAP

You need to use the new Object Services of the SAP Web AS 6.20 in your ABAP Objects programs.

Use

In principle, ABAP programs work with data and objects that are valid at runtime. They are transient – that is, temporary – and disappear when the program ends. If this data is to be stored permanently and independently of the program – that is, persistently – it must be stored in a database. (Theoretically, you could also use files at operating system level.)

Partner

Persistence Services

SAP

Business Example

Only

Internal

Internal

This lesson shows how you can use ABAP Objects to write instances of global classes to database tables, permanently and independently of a specific program. After introducing the concepts involved and how they can be applied in the SAP Web AS 6.20, we will then present a detailed description of the standard process for application developers.

08-03-2004


369


BC401

Partner

Only

Internal

SAP Internal

To ensure that the instances of persistent classes are unique, they should contain key attributes. These can be typed either as worldwide unique identification numbers (object GUID) or as semantic keys.

370


08-03-2004

Only

To use the Persistence Service for objects, their types must be created as persistent classes in the Class Builder. The term persistent class indicates that the instances of the class and their state are managed by the Persistence Service. (Global classes as such are generally persistent. The question is whether or not their instances are also persistent.)

Partner

Persistent Objects as Instances of Special Global Classes

SAP

The Persistence Services are used with object-oriented programming techniques. In this way, you can simulate an object-oriented database management system using a relational database management system and ABAP Objects.

Use

For this purpose, the Persistence Services for ABAP Objects were introduced in the SAP Web AS 6.10. On request, these services write the current attribute values of objects defined as persistent to the associated transparent tables. On receiving another request, they import these values from the tables and write the attributes to an object previously defined as persistent. When doing this, the Persistence Services use the ABAP Open SQL interface.

Use

Figure 163: Simulation of an Object-Oriented Database Management System

BC401


Only Partner

Use

In the program, you need to define a reference variable with the type of the class actor and fill it with the reference from the static attribute AGENT. You can then create a new instance of the persistent class using its method CREATE_PERSISTENT. Its interface is created from the definition of the key attributes of the persistent class. If the object already exists, it raises the class-based exception CX_OS_OBJECT_EXISTING. By default, the data is saved by asynchronous update. This process must be started using the COMMIT WORK statement. Thus, the instances of the persistent class do not become persistent objects until after that point.

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When you create a persistent class ZCL_, the Class Builder automatically generates methods for getting and setting its attributes. In addition, other Repository objects are also generated, including the class actor (also known as the class agent) ZCA_. Programs must call the methods of this class to manage the instances of persistent classes – that is, persistent objects. This class also performs the actual database access. It automatically inherits the required methods from the basis class ZCB_. These methods can be redefined if necessary – for example, to extend database accesses. The class actor is a singleton instance and has a friendship relationship with the persistent class.

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Figure 164: Generating and Writing to Persistent Objects

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You can load persistent objects (back) into a program using the GET_PERSISTENT method. When doing so, you must pass the key values to the interface parameters so that the object can be uniquely reconstituted. If the program could not find the object, it raises the class-based exception CX_OS_OBJECT_NOT_FOUND.

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Figure 165: Reading Persistent Objects

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1.

Model the class for your persistent objects.

2.

Find or create a suitable transparent table that has a field for each attribute of the class. If necessary, adapt the attributes of the class to match the technical field attributes of the transparent table. Each key attribute of the class must match a primary key field in the table and the other way round.

3.

In the Class Builder, create a persistent class as described in the SAP Library. Define the persistence mapping to the table.

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Creating Persistent Classes

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Lesson Summary You should now be able to: • Create persistent objects using the standard technique • Load persistent objects using the standard technique • Access components of persistent objects

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Related Information

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... is available in the SAP Library.

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Unit Summary

Unit Summary

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You should now be able to: • Describe the functions of the Class Builder • Create global classes using the Class Builder • Create interfaces using the Class Builder • Reference global classes/interfaces in other Repository objects • Create object-oriented transactions (transaction-code-type) • Define abstract classes • Define abstract methods • Define final classes • Define final methods • Limit the visibility of the constructor • Define friend relationships between classes • Create persistent objects using the standard technique • Load persistent objects using the standard technique • Access components of persistent objects

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Test Your Knowledge


Which of the following statements are correct?

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F

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G

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H

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I

For a user to be able to execute an object-oriented program, you always need to supply a module pool program or a function group program. Otherwise, there is nowhere for the CREATE OBJECT statement to create the instance. Determine whether this statement is true or false.

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□

You can create function modules using the Class Builder. A global class can contain a local class. A global interface can contain a local interface. A global class can contain a local interface. Nested definition of classes is when a local class is within a global class. Using the Class Builder, a local class can be converted into a global class. A local class can be copied using the Class Builder. The copy is then a global class. You can use the Refactoring Assistant to move the methods to a different class within an inheritance hierarchy. You can use the Refactoring Assistant to design model diagrams.

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A B C D E

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□ □ □ □ □

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True False

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Which of the following statements are correct? Choose the correct answer(s).

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A non-abstract class can contain abstract methods. An abstract class contains no implementations. An abstract method contains no implementations. Final classes cannot be superclasses within a class hierarchy. A final method must be redefined. Final classes can contain non-final methods. A friend of a class is also a friend of its subclasses. The subclasses of a class’s friend are also the class’s friend. The visibility of an instance constructor can be limited. A private instance constructor (instantiation only by the class itself) can be defined in the private section.

For what purpose is the technique of persistent objects used?

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C

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D

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E

To encapsulate database accesses in an object-oriented manner. Exclusively to implement database accesses in an object-oriented context (Open SQL is not allowed in ABAP Objects). To apply an object-oriented model for business objects (creating, using, writing, and reading business objects). To extend SAP standard classes (which have generally been migrated in the SAP Web AS 6.10). For authorization checks (accessing components of persistent objects is only possible using agents).

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A B

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A B C D E F G H I J

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Test Your Knowledge

Answers 1.

Which of the following statements are correct? Answer: B, D, G, H Refer to the relevant section of the lesson.

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For a user to be able to execute an object-oriented program, you always need to supply a module pool program or a function group program. Otherwise, there is nowhere for the CREATE OBJECT statement to create the instance.

The creation of the first instance and the call of the first method can be realized using an OO transaction. However, certain restrictions apply. Refer to the relevant section of the lesson. Which of the following statements are correct?

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3.

Answer: C, D, H, I

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Refer to the relevant section of the lesson. 4.

For what purpose is the technique of persistent objects used? Answer: A, C Refer to the relevant section of the lesson.

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Answer: False

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2.

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Unit Overview

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Unit Objectives After completing this unit, you will be able to:

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Unit Contents Lesson: Exception Handling in ABAP Objects for the SAP Web Application Server 6.20 .......................................................................... 383

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Create exception classes Trigger class-based exceptions in ABAP Objects programs Propagate class-based exceptions in ABAP Objects programs Handle class-based exceptions in ABAP Objects programs Map class-based exceptions in ABAP Objects programs to each other Dynamically create objects Dynamically access class and object components Define field symbols Define data references Dereference data references Dynamically create data objects Ascertain the attributes of data objects at runtime

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• • • • • • • • • • • •

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This last unit will look at the new exception concept and the language’s features for dynamic programming, thereby demonstrating how closely the procedural and object-oriented parts of ABAP Objects are interlocked. To fully exploit the available functions, you must therefore program in a partially object-oriented manner, even if you use the concepts in purely procedural program units.

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Exception Handling and Dynamic Programming

Unit 5: Exception Handling and Dynamic Programming

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Procedure: Define global exception classes ................................ 389 Exercise 23: Class-Based Exceptions ....................................... 401 Exercise 24: Mapping Exceptions to Each Other .......................... 411 Lesson: Dynamic Programming with ABAP Objects for the SAP Web Application Server 6.20 ............................................................ 422 Exercise 25: Type Casting with Data Elements (Optional)................ 443 Exercise 26: Creating Data Objects at Runtime............................ 449

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Lesson: Exception Handling in ABAP Objects for the SAP Web Application Server 6.20

Lesson: Exception Handling in ABAP Objects for the SAP Web Application Server 6.20 Lesson Overview


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Create exception classes Trigger class-based exceptions in ABAP Objects programs Propagate class-based exceptions in ABAP Objects programs Handle class-based exceptions in ABAP Objects programs Map class-based exceptions in ABAP Objects programs to each other

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You need to use the new exceptions concept of the SAP Web AS 6.20 in your ABAP Objects programs.

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We use the term exception to refer to a situation that arises while a program is being executed, where there is no point in continuing to run the program in the normal way. The SAP Web AS 6.10 introduced a new ABAP Objects exception concept, parallel to the existing concept. Exceptions and exception handling are now based on classes. This concept includes the concepts that preceded it but also enhances (and thus replaces) them.

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The Concept of Class-Based Exception Handling

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Business Example

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This lesson provides a comprehensive introduction to the new class-based exception concept in ABAP Objects. The main properties and the activities you need to perform are presented in detail and then applied in practical examples.


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You can define exception classes yourself, but there is already a range of predefined exception classes in the system – particularly for exceptions in the runtime environment. Generally you create exception classes globally in the Class Builder, but you can also define local exception classes within a program or global class. The use of class-based exceptions is not limited to object-oriented contexts. Class-based exceptions can be raised and handled in all processing blocks. In particular, the catchable runtime errors used previously can now be handled as class-based exceptions. If a class-based exception is raised, the system interrupts the normal program flow and tries to navigate to a suitable handler. If it cannot find a handler, a runtime error occurs.

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When handling an exception, you can have it raise new exceptions and thus create a chain of exceptions. Thus, in special cases, you can catch a runtime exception and then have it raise an exception of its own.

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In an exception situation, an exception is represented by an exception object that is, an instance of an exception class. The attributes of each exception object contain information about the error situation.

SAP

Class-based exceptions are raised either using the ABAP statement RAISE EXCEPTION or by the ABAP runtime environment. Division by zero, for example, would be an example of the latter.

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Figure 166: An Overview of the Class-Based Exception Concept

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All exception classes are derived from the one of the classes CX_NO_CHECK, CX_DYNAMIC_CHECK, or CX_STATIC_CHECK, themselves derived from the common superclass CX_ROOT.

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The way in which exception classes are assigned to one of these three paths in the hierarchy defines how the associated exceptions are propagated. (This will be discussed in more detail later in this unit.)

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New exception classes inherit from one of these superclasses, so that other components can be added. These are usually individual exception texts. You can assign several texts to each class. The IDs assigned to them are created by the Class Builder as identically-named static constants. You can then specify which text is to be used when an exception is raised by passing one of these constants to the import parameter TEXTID of the instance constructor.

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The CX_ROOT class provides some predefined methods that are inherited by all exception classes: The GET_SOURCE_POSITION method returns the name of the main program and (if relevant) the names of the include program and the line number in the source code where the exception occurred. The GET_TEXT method returns an exception text in the form of a string.

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In the SAP standard system, the names of all exception classes start with CX_.

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Figure 167: Exception Classes: The Inheritance Hierarchy


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All exception classes inherit the KERNEL_ERRID attribute from CX_ROOT. This attribute contains the name of the appropriate runtime error if the exception was raised by the runtime environment - such as BCD_ZERODIVIDE if the program catches a CX_SY_ZERODIVIDE exception (division by zero). If the exception is not listed, a runtime error occurs. An exception can only be handled if the statement that could raise it is enclosed in a TRY-ENDTRY block. The exception is then handled using the CATCH statement in the TRY-ENDTRY block.

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A CATCH block contains the exception handler that is executed if a specified exception has occurred in the associated TRY-ENDTRY block. You can specify any number of exception classes to the CATCH statement. In this way, you define an exception handler for all these exception classes and their subclasses. Like all ABAP control structures, TRY-ENDTRY structures can be nested to any depth. Thus the TRY block, CATCH blocks, and the CLEANUP block in particular can contain complete TRY-ENDTRY blocks themselves.

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The TRY block contains the set of statements that handle the exceptions. If an exception occurs in the TRY block, the system searches first for a CATCH statement (which will handle the exception) in the same TRY-ENDTRY block and then step by step outwards in all the enclosing TRY-ENDTRY blocks. If it finds one, it navigates to this handler. If it cannot find a handler but the TRY-ENDTRY structure is in a procedure, it then tries to propagate the exception to the calling program. (This will be discussed in more detail later.)

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Figure 168: Structure of a TRY-ENDTRY Block

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After an exception occurs, the system searches through the listed exception handlers in the order specified. It then executes the first exception handler whose CATCH statement contains the relevant exception class or one of its superclasses.

In the following sections, we will focus on global exception classes that are handled locally. Remember, you can also use local exception classes handled locally or global exception classes handled in methods of other global classes.

There are two special features to note in the following example: Firstly, we will simply instantiate a standard exception class, rather than define a new one. Secondly, the exception will be raised by the runtime system as the result of an error, rather than by a procedure.

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Example: Handling a Predefined Exception

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In some cases, the system cannot find a handler for an exception within a specific TRY-ENDTRY block but the exception is handled in a surrounding TRY-ENDTRY block or propagated to a calling program. If this occurs, a CLEANUP block is executed before leaving the TRY-ENDTRY block.

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Figure 169: Example Syntax for Handling Predefined Exceptions

In the above calculation, if the value range for data type I is exceeded, the runtime system raises the exception CX_SY_ARITHMETIC_OVERFLOW. This exception is handled in the implemented CATCH block. The reference to the appropriate instance is stored in the data object REF_EXC. The handler

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can then access the instance’s exception text using the functional method GET_TEXT. The text is stored in the data object TEXT with the type STRING and then displayed as an information message. Note: The MESSAGE statement was extended in SAP Web AS 6.10, so that any string could be sent as a data object with the type STRING.

As well as the string message that will be displayed, you must also specify the message type message_type.

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The ABAP keyword documentation for each statement lists the classes whose exceptions may occur when that statement is executed. The following will show you how to create your own global exception classes.

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As with the (obsolete) use of CATCH SYSTEM-EXCEPTIONS, this is also about catching runtime errors that cannot be entirely excluded. A typical example of this can be found in widening cast assignments.

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Caution: This is a demonstration example that has been deliberately kept simple. Normally, you would define the RESULT variable with numerical type F to avoid a runtime error. Then you could define the size of the result value before, if necessary using MOVE to convert to an integer variable.

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The class CX_SY_ARITHMETIC_OVERFLOW is a subclass of the classes CX_SY_ARITHMETIC_ERROR, CX_DYNAMIC_CHECK, and CX_ROOT. Thus the exception raised above can also be handled if you enter one of these classes after the CATCH statement.

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If the value range for data type I is not exceeded, no exception is raised and the TRY block is processed completely. The processing block then continues executing after the keyword ENDTRY.

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MESSAGE string TYPE message_type.

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Define global exception classes 1.

In the Class Builder, create a global class as described in the SAP Library. When you enter its name, prefix it with CX_. Choose the option Exception Class as the Class Type. Do not change the default entry for Superclass, unless you are fully aware of the consequences of doing so.

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Use Internal

Give your exception class additional attributes as necessary (for example, for generic extensions to exception texts). If these attributes are public, the Class Builder generates an appropriate instance constructor so that these values can be set for these attributes when the exception is raised. The import parameters are generated with the same names as the attributes.

3.

Save as many exception texts as you need. When doing so you can insert your attributes as parameters in the static text in the form &&.

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2.

For the first text you create yourself, always use a predefined static constant as an ID. It always has the same name as the exception class itself. If no text is specified explicitly when the exception is raised, the text with this ID is used instead. For all other texts, you define other IDs. The Class Builder then generates identically-named static constants Continued on next page

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Figure 170: Creating Global Exception Classes

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automatically. When the exception is raised, you pass one of these constants to the import parameter TEXTID, to specify the appropriate text for the exception instance.

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Figure 171: Define Variable Exception Texts

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Activate your exception class.

Propagating and Handling an Exception Exceptions that occur in procedures do not necessarily need to be handled where they occur; they can be propagated to the caller of the procedure. The caller can then handle the exception itself or propagate it to its own caller, and so on. The highest levels to which an exception can be propagated are processing blocks without local data areas – that is, event blocks or dialog

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4.

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Note: The exception texts of global exception classes are stored in their translations in the Open Text Repository (OTR). Note that several texts can be assigned to a single class. You assign a text to an exception using the TEXTID attribute, which contains the globally unique ID of the text object in the OTR in an instance at runtime. The method GET_TEXT then exports this text, replaces any text parameters with the contents of the relevant attributes as necessary, and returns the text as a character string.

BC401


modules. The exceptions propagated by the called procedures must be dealt with there, as must any exceptions raised within this processing block itself. Otherwise a runtime error occurs. To propagate an exception from within a procedure, you generally need to include the RAISING addition in the procedure’s signature. In methods of local classes and subroutines, specify the RAISING addition directly when defining the procedure

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FORM subr_name ... RAISING cx_... cx_.... After RAISING, you list the exception classes whose objects are to be propagated. In methods of global classes, the exception classes whose instances are to be propagated are entered in the exception table of the method in the Class Builder. You also need to set the Exception Class flag for each exception table. The process is similar for function modules. To set the flag in the Function Builder, choose the Exceptions tab. It is clear that a global method or function module can raise only class-based or conventional exceptions.

Internal

FORM subr_name ... RAISING cx_... cx_... or

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Figure 172: Propagating Exceptions

The TEXTID parameter is optional: The default value is always the static constant, which has the same name as the exception class. However, one of the static constants defined as additional text IDs in the exception class can also be

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used to supply the value. When the exception is raised, the appropriate text for that exception instance is raised. After the exception has been caught, you can then display the text using the functional method GET_TEXT. If the caller does not catch the exception, it can be propagated upwards to the next-level caller. Before control is passed to the next-level caller, the (optional) CLEAN-UP block may be executed. You then use this block to run the appropriate statements.

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CLASS lcl_plane DEFINITION.

Internal

Example: Raising, Passing Along, and Handling an Exception

PUBLIC SECTION.

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...

METHODS get_attributes

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EXPORTING ex_name

TYPE t_name_15

value(ex_wa_plane) TYPE saplane RAISING

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ENDCLASS.

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cx_bc401_excd_planetype.

"lcl_plane DEFINITION

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CLASS lcl_plane IMPLEMENTATION. ...

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METHOD get_attributes.

SELECT SINGLE * FROM saplane INTO ex_wa_plane WHERE planetype = me->type. IF sy-subrc = 0. IF ex_wa_plane-seatsmax_b = 0. "should stand for freighter here RAISE EXCEPTION TYPE cx_bc401_excd_planetype EXPORTING planetype = me->type

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textid = cx_bc401_excd_planetype=>cx_bc401_excd_planetype_f. ENDIF. ELSE. RAISE EXCEPTION TYPE cx_bc401_excd_planetype EXPORTING planetype = me->type. ENDIF. "lcl_plane

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ENDMETHOD.

"lcl_plane IMPLEMENTATION

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CLASS lcl_carrier DEFINITION. PUBLIC SECTION.

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...

ENDCLASS.

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METHODS display_attributes. "lcl_carrier DEFINITION

CLASS lcl_carrier IMPLEMENTATION.

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... METHOD display_attributes. DATA:

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l_ref_plane TYPE REF TO lcl_plane, l_name TYPE t_name_15, l_wa_plane TYPE saplane,

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l_ref_exc TYPE REF TO cx_bc401_excd_planetype, l_exc_text TYPE string.

... TRY.

CALL METHOD l_ref_plane->get_attributes IMPORTING

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ex_wa_plane = l_wa_plane. WRITE: l_wa_plane-planetype, l_wa_plane-producer, l_wa_plane-seatsmax_b. CATCH cx_bc401_excd_planetype INTO l_ref_exc. l_exc_text = l_ref_exc->get_text( ). WRITE l_exc_text COLOR COL_NEGATIVE.

ENDMETHOD.

"display_attributes "lcl_carrier IMPLEMENTATION

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Hint: It would also have been possible to deal with the two errors by means of two exception classes. You could then use different CATCH blocks to deal with whichever of the two errors occurred. However, at this point we wanted to demonstrate how you would use different texts within one exception class.

Partner

The exception is handled in the instance method DISPLAY_ATTRIBUTES of the class LCL_CARRIER. If the exception is raised, execution of the method GET_ATTRIBUTES terminates, and continues with the execution of the CATCH block. Note in particular that the program no longer executes the WRITE statements entered in the TRY block after the method call. The system copies the reference to the instance of the exception class to the local variable L_REF_EXC. The exported error text is set dynamically so that it contains context-sensitive information.

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The instance method GET_ATTRIBUTES of the local class LCL_PLANE displays the name and other attributes of the airplane. If the airplane type is not valid, the exception you defined yourself, CX_BC401_EXCD_PLANETYPE, is to be raised and propagated. That is, there may be instances of airplanes in this scenario whose type is not valid. For example, there may be no data for the airplane type in the table SAPLANE or the airplane may be a freight aircraft. The exception class is written so that there is a separate text available for each of these two situations. In one of the two cases, the default value is passed to the parameter TEXTID, while in the other an additionally defined static constant is passed, depending on the cause of the error. In both cases, the program also passes the invalid airplane type itself to the exception instance.

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ENDCLASS.

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ENDTRY.

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Class-Based Exceptions in Debugging Mode If an exception is raised, the name of the exception class is displayed in the Exception Raised field in debugging mode. If this exception is caught using a CATCH block, this is displayed in the form of a success message. The pointer for the current statement then moves to this CATCH block.

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Exception Classes: The Inheritance Hierarchy The following explains consequences that arise from the choice of an exception class’s superclass. It also shows how the exceptions in the runtime system were integrated into the inheritance hierarchy of the exception classes.

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Two pushbuttons also appear. They allow you to display the values of the attributes of the exception instance and navigate to the point in the source code where the exception occurred.

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Figure 173: Class-Based Exceptions in Debugging Mode


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For subclasses of CX_NO_CHECK, the rule is that the corresponding exceptions cannot be propagated explicitly using the RAISING addition. These exceptions can be handled. Otherwise they are automatically propagated. Neither a syntax warning nor a runtime error is caused directly where it is raised. Instead all exceptions that are not handled somewhere in the call hierarchy are propagated up to the highest call level. If it is not

Partner

The rule for subclasses of CX_DYNAMIC_CHECK also applies to subclasses of CX_DYNAMIC_CHECK: You must either handle them or explicitly propagate them using the RAISING addition. The difference is that this is not checked statically. That is, the system does not report a syntax warning, if the exception is not either handled or propagated. If the exception is then raised, a runtime error occurs. Typical examples of this situation are the predefined exceptions CX_SY_... for errors that occur in the runtime environment. These are usually subclasses of CX_DYNAMIC_CHECK.

SAP

Subclasses of CX_STATIC_CHECK: The relevant exception must either be handled, or propagated explicitly using the RAISING addition. If this is not the case, the syntax check displays a warning. If you define your own exception classes, CX_STATIC_CHECK is defined as the superclass by default.

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Figure 174: Integration of Standard Exceptions in the Runtime System

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caught there either, a runtime error occurs at that point. Some predefined exceptions with the prefix CX_SY_... for error situations in the runtime environment are subclasses of CX_NO_CHECK.

Mapping Exceptions to Each Other

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In the following section, you should show how the raising of exceptions can be chained together – that is, how an exception raises another exception, and so on. Each instance should remain valid, regardless of whether or not the associated CATCH block has already been left or not. In this respect, you must make sure that the previous exception instance can always be accessed by means of at least one reference. The public instance attribute PREVIOUS, inherited by all exception classes from CX_ROOT, provides a convenient way of doing this.

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For the sake of clarity, you should start by emphasizing that an exception can be propagated through any number of call hierarchies, before it is finally handled.

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Figure 175: Mapping Exceptions to Each Other

When raising the next exception, only one reference to the previous exception instance must be passed to the new instance. You do this with the optional parameter PREVIOUS of the instance constructor – that is, using RAISE

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EXCEPTION. In this way, the new exception is mapped to the previous one. After the mapped exception has been caught, the instance attribute PREVIOUS contains a reference to the previous exception instance, and so on. In this way, you can access each instance in the chain of exceptions. Therefore, you can follow the history of the raising of the exceptions in the program.

Example: Creating a Chain of Exceptions

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CLASS lcl_carrier

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DEFINITION.

Internal

The method GET_ATTRIBUTES has been defined and implemented in the local class LCL_PLANE as in the previous example. Another exception class, here CX_BC401_EXCD_LIST, has already been defined.

PUBLIC SECTION.

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...

METHODS display_attributes

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RAISING cx_bc401_excd_list.

ENDCLASS.


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CLASS lcl_carrier IMPLEMENTATION. ...

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METHOD display_attributes. DATA: l_ref_plane TYPE REF TO lcl_plane, l_name TYPE t_name_15,

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l_wa_plane TYPE saplane,

l_ref_exc TYPE REF TO cx_bc401_excd_planetype, l_exc_text TYPE string.

... TRY. CALL METHOD l_ref_plane->get_attributes IMPORTING

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ex_wa_plane = l_wa_plane. WRITE: l_wa_plane-planetype, l_wa_plane-producer, l_wa_plane-seatsmax_b. CATCH cx_bc401_excd_planetype INTO l_ref_exc. l_exc_text = l_ref_exc->get_text( ). WRITE l_exc_text COLOR COL_NEGATIVE. RAISE EXCEPTION TYPE cx_bc401_excd_list

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EXPORTING previous = l_ref_exc. ENDTRY.

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ENDMETHOD.

"display_attributes

ENDCLASS.


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... DATA: ref_plane

TYPE REF TO lcl_plane,

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ref_exc exc_text

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ref_carrier TYPE REF TO lcl_carrier,

TYPE REF TO cx_bc401_excd_list, TYPE string,

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previous_text TYPE string.

...

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START-OF-SELECTION. ...

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TRY. CALL METHOD ref_carrier->display_attributes. CATCH cx_bc401_excd_list INTO ref_exc.

exc_text = ref_exc->get_text( ). MESSAGE exc_text TYPE ’I’.

previous_text = ref_exc->previous->get_text( ). MESSAGE previous_text TYPE ’I’. ENDTRY.

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...

Since the method DISPLAY_ATTRIBUTES propagates its exception to the main program, the system stops list processing within the DISPLAY_ATTRIBUTES method as soon as the first error occurs.

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SAP

Hint: It would also be possible to propagate the original exception from the method DISPLAY_ATTRIBUTES. We would not then have had to define two exception classes explicitly. However, the point of this example is to show how exceptions can be chained.

Use

Partner

The exception for the list with the errors is now handled in the main program. First the exception text is displayed as an information message. However, since the exception is mapped to a second exception for the invalid airplane type, the instance attribute PREVIOUS contains a reference to the second exception. You use this reference to export the text from the original exception and display it as an information message.

Internal

Only

The exception for the invalid airplane type is caught in the instance method DISPLAY_ATTRIBUTES of the class LCL_CARRIER. The exception text is displayed in the list. Another exception is then raised, since the list now contains errors. The reference to the first exception instance is now passed to the second.

Only

Internal

Use

Partner

400


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BC401


Exercise 23: Class-Based Exceptions Exercise Objectives

Only

Business Example

Use

Partner

Your airplane management program should use the class-based exception concept if an invalid airplane type occurs. An error text should be displayed in the list, instead of the current default values.

Task 1:

Use

Create a global exception class called ZCX_##_INVALID_PLANETYPE. (where ## is your two-digit group number). Choose the superclass so that the syntax check determines if the relevant exception is handled after it is raised or if it is explicitly propagated.

2.

Add an attribute for the airplane type (suggested name: PLANETYPE) and assign the type S_PLANETYPE to it.

3.

Create a default error message that can be enhanced dynamically to include the airplane type.

Partner

Task 2: Raise your new exception if an error occurs. 1.

Complete your program ZBC401_##_MAIN program or copy the model solution for the airplane management program, SAPBC401_EVES_MAIN_B (where ## is your two-digit group number).

2.

Raise your exception within method ET_TECHNICAL_ATTRIBUTES of local class LCL_AIRPLANE. Ensure that the invalid airplane type is copied into the attribute of the exception instance. Continued on next page


401

Only

Internal

1.

SAP

SAP

Create a global exception class for an invalid airplane type.

08-03-2004

Internal

After completing this exercise, you will be able to: • Define global exception classes • Raise class-based exceptions • Propagate class-based exceptions • Handle class-based exceptions


3.

BC401

Make sure that the raised exception is explicitly propagated.

Task 3: Handle the exception. 1.

Catch your exception in the DISPLAY_ATTRIBUTES method of local class LCL_AIRPLANE.

Only

2.

Read the error text in the exception instance and display it in the ABAP list.

Use

Partner

To that end, define a variable (suggested name: EXC_TEXT) with data type STRING.

Internal

To do so, define a local reference variable (suggested name: R_EXCEPTION) and assign it to the CX_ROOT class.

SAP

SAP Only

Internal

Use

Partner

402


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BC401


Solution 23: Class-Based Exceptions Task 1: Create a global exception class for an invalid airplane type. Create a global exception class called ZCX_##_INVALID_PLANETYPE. (where ## is your two-digit group number). Choose the superclass so that the syntax check determines if the relevant exception is handled after it is raised or if it is explicitly propagated. a)

2.

Add an attribute for the airplane type (suggested name: PLANETYPE) and assign the type S_PLANETYPE to it. a) b)

SAP

Create a default error message that can be enhanced dynamically to include the airplane type. a)

Follow the processes as outlined in the relevant section of this document. Speak to your instructor if you have any questions.

Task 2: 1.

Complete your program ZBC401_##_MAIN program or copy the model solution for the airplane management program, SAPBC401_EVES_MAIN_B (where ## is your two-digit group number). a) b)

2.

Carry out this step in the usual manner. Additional information is available in the SAP Library. Model solution: SAPBC401_EXCS_RAISE_TRY

Raise your exception within method ET_TECHNICAL_ATTRIBUTES of local class LCL_AIRPLANE.


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403

Only

Internal

Raise your new exception if an error occurs.

Partner

b)

Use

Follow the processes as outlined in the relevant section of this document. Speak to your instructor if you have any questions.

SAP

3.

Use

Partner

b) c)

Follow the processes as outlined in the relevant section of this document. Speak to your instructor if you have any questions. Model solution: CX_BC401_INVALID_PLANETYPE

Internal

Only

1.


BC401

Ensure that the invalid airplane type is copied into the attribute of the exception instance. a) 3.


Make sure that the raised exception is explicitly propagated. a)


Handle the exception. 1.

Catch your exception in the DISPLAY_ATTRIBUTES method of local class LCL_AIRPLANE.

a) 2.


Read the error text in the exception instance and display it in the ABAP list.

SAP

a)


SAP

To that end, define a variable (suggested name: EXC_TEXT) with data type STRING.

Use

Partner

To do so, define a local reference variable (suggested name: R_EXCEPTION) and assign it to the CX_ROOT class.

Internal

Only

Task 3:


*&---------------------------------------------------------------------* *&

Include

BC401_EXCS_RAISE_TRY_CL2

*

*&---------------------------------------------------------------------* *------------------------------------------------------------------* * events in: lcl_airplane and lcl_carrier ! *

*------------------------------------------------------------------* *


*

*------------------------------------------------------------------* CLASS lcl_airplane DEFINITION.


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Only

Internal


Partner

Use

Result

BC401


PUBLIC SECTION. "--------------------------------------------CONSTANTS: pos_1 TYPE i VALUE 30. METHODS: constructor IMPORTING im_name

TYPE string


Internal

Only

display_attributes.

CLASS-METHODS: display_n_o_airplanes. EVENTS: airplane_created.

Partner

PRIVATE SECTION. "---------------------------------------------METHODS: get_technical_attributes EXPORTING ex_weight ex_tankcap

DATA: name

TYPE s_plan_wei TYPE s_capacity

cx_bc401_invalid_planetype.

SAP

SAP

RAISING


Use

IMPORTING im_type

TYPE string,


ENDCLASS.

Partner

Use


*------------------------------------------------------------------*

Internal

*


*


Only

METHOD constructor. name

= im_name.

planetype

= im_planetype.

n_o_airplanes = n_o_airplanes + 1. RAISE EVENT airplane_created. ENDMETHOD.

"constructor

METHOD display_attributes. DATA: weight TYPE saplane-weight,


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BC401

cap TYPE saplane-tankcap, r_exception TYPE REF TO cx_root, exc_text TYPE string.

WRITE: / icon_ws_plane AS ICON, / ’Name of Airplane’(001), AT pos_1 name, / ’Type of airplane: ’(002), AT pos_1 planetype.

Internal

Only

* handle exception in case of invalid planetype: TRY. get_technical_attributes( EXPORTING im_type = planetype IMPORTING ex_weight = weight ex_tankcap = cap ).

Partner

WRITE: / ’Weight:’(003), weight, ’Tankkap:’(004), cap. CATCH cx_bc401_invalid_planetype INTO r_exception.

Use

exc_text = r_exception->get_text( ). WRITE: / exc_text COLOR COL_NEGATIVE. ENDTRY. "display_attributes

SAP

SAP

ENDMETHOD. METHOD display_n_o_airplanes.

WRITE: /, / ’Number of airplanes: ’(ca1), AT pos_1 n_o_airplanes LEFT-JUSTIFIED, /. "display_n_o_airplanes

Partner

Use

ENDMETHOD.


Internal

WHERE planetype = im_type. IF sy-subrc 0. RAISE EXCEPTION TYPE cx_bc401_invalid_planetype

Only

EXPORTING planetype = im_type. ENDIF. ENDMETHOD.

ENDCLASS.



*---------------------------------------------------------------------* *



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*---------------------------------------------------------------------* * *---------------------------------------------------------------------* CLASS lcl_cargo_plane DEFINITION INHERITING FROM lcl_airplane. PUBLIC SECTION. "---------------------METHODS: constructor IMPORTING im_name TYPE string

Internal

Only

im_planetype TYPE saplane-planetype im_cargo TYPE scplane-cargomax. METHODS: display_attributes REDEFINITION. PRIVATE SECTION.

Partner

"---------------------DATA: max_cargo TYPE scplane-cargomax.

"lcl_cargo_plane DEFINITION

Use

ENDCLASS.

*---------------------------------------------------------------------* *


SAP

SAP

*---------------------------------------------------------------------* * *---------------------------------------------------------------------* CLASS lcl_cargo_plane IMPLEMENTATION.

Partner

Use

METHOD constructor. CALL METHOD super->constructor EXPORTING im_name

= im_name

Internal

im_planetype = im_planetype. max_cargo = im_cargo. ENDMETHOD.

"constructor

Only

METHOD display_attributes. super->display_attributes( ). WRITE: / ’Max Cargo = ’, max_cargo. ULINE. ENDMETHOD. ENDCLASS.

"display_attributes "lcl_cargo_plane IMPLEMENTATION

*---------------------------------------------------------------------*


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*

BC401


*---------------------------------------------------------------------* * *---------------------------------------------------------------------* CLASS lcl_passenger_plane DEFINITION INHERITING FROM lcl_airplane.. PUBLIC SECTION. METHODS: constructor IMPORTING im_name TYPE string

Internal

Only

im_planetype TYPE saplane-planetype im_seats TYPE sflight-seatsmax. METHODS: display_attributes REDEFINITION. PRIVATE SECTION. "lcl_passenger_plane DEFINITION

*---------------------------------------------------------------------* *


*---------------------------------------------------------------------* *

SAP

CLASS lcl_passenger_plane IMPLEMENTATION. METHOD constructor.

SAP

*---------------------------------------------------------------------*

Use

Partner

DATA: max_seats TYPE sflight-seatsmax. ENDCLASS.

CALL METHOD super->constructor

Partner

Use

EXPORTING im_name

= im_name

im_planetype = im_planetype. max_seats = im_seats.

Internal

ENDMETHOD.

"constructor


Only

super->display_attributes( ). WRITE: / ’Max Seats = ’, max_seats. ULINE. ENDMETHOD. ENDCLASS.

"display_attributes "lcl_passenger_plane IMPLEMENTATION

*---------------------------------------------------------------------* *


*---------------------------------------------------------------------* *


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*---------------------------------------------------------------------* CLASS lcl_carrier DEFINITION. PUBLIC SECTION. "---------------------------------------INTERFACES lif_partners. METHODS: constructor IMPORTING im_name TYPE string, get_name RETURNING value(ex_name) TYPE string,

Internal

Only

add_airplane FOR EVENT airplane_created OF lcl_airplane IMPORTING sender, display_airplanes, display_attributes.

Partner

PRIVATE SECTION. "----------------------------------DATA: name

TYPE string,

ENDCLASS.

Use

airplane_list TYPE TABLE OF REF TO lcl_airplane. "lcl_carrier DEFINITION

*---------------------------------------------------------------------*

SAP


SAP

*

*---------------------------------------------------------------------* CLASS lcl_carrier IMPLEMENTATION. METHOD lif_partners~display_partner. display_attributes( ).

Use

Partner

ENDMETHOD.


METHOD add_airplane. APPEND sender TO airplane_list.

Internal

ENDMETHOD.

"add_airplane


Only

SKIP 2. WRITE: icon_flight AS ICON, name . ULINE. ULINE. display_airplanes( ). ENDMETHOD.

"display_attributes

METHOD display_airplanes. DATA: r_plane TYPE REF TO lcl_airplane. LOOP AT airplane_list INTO r_plane. r_plane->display_attributes( ). ENDLOOP.


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409


ENDMETHOD.

BC401

"display_airplanes

METHOD constructor. name = im_name. SET HANDLER add_airplane FOR ALL INSTANCES. RAISE EVENT lif_partners~partner_created. ENDMETHOD.

"constructor

Internal

Only



Use

Partner

ENDCLASS.

"get_name

SAP

SAP Only

Internal

Use

Partner

410


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BC401


Exercise 24: Mapping Exceptions to Each Other Exercise Objectives

Only

If your airplane management program encounters an exception and displays an error on the list, make the program raise another exception. The second exception should refer to the first exception, so that both instances can be evaluated when the exception is handled.

SAP Internal

Complete your ZBC401_##_MAIN program or copy the sample solution of the previous exercise, SAPBC401_EXCS_RAISE_TRY. (where ## is your two-digit group number).

2.

To make your program easier to maintain, create another include program for your exception class and include it in your main program (suggested name: ZBC401_##_EXCEPTION).

3.

Define a local exception class in your new include program. The exception is needed in case exception handling takes place during the output of the list (suggested name: LCX_LIST_ERROR). Hint: Derive your local exception class from the superclass CX_STATIC_CHECK.


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411

Only

1.

Partner

Use

Define a local exception class for the event of an error text being displayed in the list.

SAP

Task 1:

Use

Partner

Business Example

Internal

After completing this exercise, you will be able to: • Define local exception classes • Map an exception, when it is raised, to another exception that has already been raised • When handling a mapped exception, evaluate the previous exception as well


4.

BC401

Add a public instance method to your local exception class. This method returns a special text appropriate to the error that may occur – for example “The list contains an error.” We suggest the name: GET_EXC_TEXT.

Task 2: Raise the new exception and map it to the original one. Raise your new exception in method DISPLAY_ATTRIBUTES of local class LCL_AIRPLANE when the exception for the invalid airplane type is being handled. Transfer the reference to the original exception instance to the exception instance that is to be created. Extend the signature of the DISPLAY_ATTRIBUTES method, so that your new exception is explicitly propagated.

Task 3:

2.

Use this reference to export the text of your new exception. Define an appropriately typed text variable for this purpose (suggested name: EXC_TEXT).

Use

Catch your new exception in the DISPLAY_AIRPLANES method of local class LCL_CARRIER. Define an appropriately-typed local reference for the purpose (suggested name: R_EXC).

Internal

If an exception occurs, display the text of your new exception as well the old one, in the form of an information message. 3.

Use the same variables to export the text of the original exception.

412


Only

Enter this text in form of an information message, as well.

Partner

1.

SAP

SAP

Handle your new exception and evaluate the information of both the new and the original exception instance.

Use

Partner

2.

Internal

Only

1.

08-03-2004

BC401


Solution 24: Mapping Exceptions to Each Other Task 1: Define a local exception class for the event of an error text being displayed in the list. Complete your ZBC401_##_MAIN program or copy the sample solution of the previous exercise, SAPBC401_EXCS_RAISE_TRY. (where ## is your two-digit group number). a)

2.

To make your program easier to maintain, create another include program for your exception class and include it in your main program (suggested name: ZBC401_##_EXCEPTION).

Define a local exception class in your new include program. The exception is needed in case exception handling takes place during the output of the list (suggested name: LCX_LIST_ERROR). Hint: Derive your local exception class from the superclass CX_STATIC_CHECK.

4.


Add a public instance method to your local exception class. This method returns a special text appropriate to the error that may occur – for example “The list contains an error.” We suggest the name: GET_EXC_TEXT. a)


Task 2: Raise the new exception and map it to the original one. 1.

08-03-2004

Raise your new exception in method DISPLAY_ATTRIBUTES of local class LCL_AIRPLANE when the exception for the invalid airplane type is being handled. Continued on next page


413

Only

Internal

a)

Partner

Use

3.


SAP

SAP

a)

Use

Partner

b)

Carry out this step in the usual manner. Additional information is available in the SAP Library. Model solution: SAPBC401_EXCS_RAISE_TRY_OPT

Internal

Only

1.


BC401

Transfer the reference to the original exception instance to the exception instance that is to be created. a) 2.


Extend the signature of the DISPLAY_ATTRIBUTES method, so that your new exception is explicitly propagated. a)


Only

Handle your new exception and evaluate the information of both the new and the original exception instance. Catch your new exception in the DISPLAY_AIRPLANES method of local class LCL_CARRIER. Define an appropriately-typed local reference for the purpose (suggested name: R_EXC). a)

Use this reference to export the text of your new exception. Define an appropriately typed text variable for this purpose (suggested name: EXC_TEXT). If an exception occurs, display the text of your new exception as well the old one, in the form of an information message. a)

Use


Use the same variables to export the text of the original exception. Enter this text in form of an information message, as well.

Internal

a)


Result

Only


SAPBC401_EXCS_RAISE_TRY_OPT REPORT

sapbc401_excs_raise_try_opt.


TYPE-POOLS icon.


414


Partner

3.

SAP

SAP

2.


Use

Partner

1.

Internal

Task 3:

08-03-2004

BC401


INCLUDE bc401_excs_raise_try_opt_exc. INCLUDE bc401_excs_raise_try_opt_cl1. INCLUDE bc401_excs_raise_try_opt_cl2.

DATA: r_vehicle TYPE REF TO lcl_vehicle, r_truck TYPE REF TO lcl_truck, TYPE REF TO lcl_bus,

Internal

Only

r_bus

r_passenger TYPE REF TO lcl_passenger_plane, r_cargo TYPE REF TO lcl_cargo_plane, r_carrier TYPE REF TO lcl_carrier, r_rental TYPE REF TO lcl_rental,

START-OF-SELECTION.

...

Use

Partner

r_agency TYPE REF TO lcl_travel_agency.

BC401_EXCS_RAISE_TRY_OPT_EXC *&---------------------------------------------------------------------* Include

BC401_EXCS_RAISE_TRY_OPT_EXC

*

SAP

SAP

*&

*&---------------------------------------------------------------------*

*---------------------------------------------------------------------*

Use

Partner

*

CLASS lcx_list_error DEFINITION

*---------------------------------------------------------------------* * *---------------------------------------------------------------------*

Internal

CLASS lcx_list_error DEFINITION INHERITING FROM cx_static_check.

PUBLIC SECTION.

Only

METHODS get_exc_text RETURNING value(result) TYPE string.

ENDCLASS.

"lcx_list_error DEFINITION

*---------------------------------------------------------------------* *

CLASS lcx_list_error IMPLEMENTATION

*---------------------------------------------------------------------* *


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415


BC401

*---------------------------------------------------------------------* CLASS lcx_list_error IMPLEMENTATION.

METHOD get_exc_text. result = ’The list contains an error.’(err). "get_text

ENDMETHOD.

"lcx_list_error IMPLEMENTATION

BC401_EXCS_RAISE_TRY_CL2 *&---------------------------------------------------------------------* *&

Include


*

Partner

*&---------------------------------------------------------------------*

*


Use

*------------------------------------------------------------------* *

*------------------------------------------------------------------*

SAP

SAP

CLASS lcl_airplane DEFINITION.

PUBLIC SECTION. "---------------------------------------------

Use

METHODS: display_attributes

im_name

Partner

Internal

CONSTANTS: pos_1 TYPE i VALUE 30. METHODS: constructor IMPORTING TYPE string

im_planetype TYPE saplane-planetype.

RAISING lcx_list_error.

Only

CLASS-METHODS: display_n_o_airplanes. EVENTS: airplane_created. PRIVATE SECTION. "---------------------------------------------METHODS: get_technical_attributes IMPORTING im_type EXPORTING ex_weight ex_tankcap RAISING

TYPE saplane-planetype TYPE s_plan_wei TYPE s_capacity

cx_bc401_invalid_planetype.


416


Internal

Only

ENDCLASS.

08-03-2004

BC401


DATA: name

TYPE string,


CLASS-DATA: n_o_airplanes TYPE i. ENDCLASS.


*


Internal

Only

*------------------------------------------------------------------* *


Partner

METHOD constructor. ... ENDMETHOD.

"constructor

Use

METHOD display_attributes. DATA: weight TYPE saplane-weight, cap TYPE saplane-tankcap,

SAP

SAP

r_exception TYPE REF TO cx_root, exc_text TYPE string. WRITE: / icon_ws_plane AS ICON, / ’Name of Airplane’(001), AT pos_1 name,

Partner

Use

/ ’Type of airplane: ’(002), AT pos_1 planetype. *

handle exception in case of invalid planetype: TRY.

Internal

get_technical_attributes( EXPORTING im_type = planetype IMPORTING ex_weight = weight ex_tankcap = cap ).

Only

WRITE: / ’Weight:’(003), weight, ’Tankkap:’(004), cap. CATCH cx_bc401_invalid_planetype INTO r_exception. exc_text = r_exception->get_text( ). WRITE: / exc_text COLOR COL_NEGATIVE. RAISE EXCEPTION TYPE lcx_list_error EXPORTING previous = r_exception.

ENDTRY.


08-03-2004


417


ENDMETHOD.

BC401

"display_attributes

METHOD display_n_o_airplanes. ... ENDMETHOD.


METHOD get_technical_attributes. SELECT SINGLE weight tankcap FROM saplane

Internal

Only

INTO (ex_weight, ex_tankcap) WHERE planetype = im_type. IF sy-subrc 0. RAISE EXCEPTION TYPE cx_bc401_invalid_planetype EXPORTING planetype = im_type.

ENDMETHOD.


ENDCLASS.


...*---------------------------------------------------------------------* *


SAP

* *---------------------------------------------------------------------* CLASS lcl_carrier DEFINITION.

Partner

Use

PUBLIC SECTION. "---------------------------------------INTERFACES lif_partners. METHODS: constructor IMPORTING im_name TYPE string,

Internal

SAP

*---------------------------------------------------------------------*

Use

Partner

ENDIF.

get_name RETURNING value(ex_name) TYPE string, add_airplane FOR EVENT airplane_created OF lcl_airplane

Only

IMPORTING sender, display_airplanes, display_attributes. PRIVATE SECTION. "----------------------------------DATA: name

TYPE string,




418


08-03-2004

BC401


*---------------------------------------------------------------------* *


*---------------------------------------------------------------------* CLASS lcl_carrier IMPLEMENTATION. METHOD lif_partners~display_partner. ... "lif_partners~display_partner

Internal

Only

ENDMETHOD. METHOD add_airplane. ... ENDMETHOD.

"add_airplane

Partner

METHOD display_attributes. SKIP 2. WRITE: icon_flight AS ICON, name . ULINE. ULINE. ENDMETHOD.

Use

display_airplanes( ). "display_attributes

METHOD display_airplanes.

SAP

r_plane

TYPE REF TO lcl_airplane,

r_exc

TYPE REF TO lcx_list_error,

SAP

DATA:

exc_text TYPE string.

Partner

Use

LOOP AT airplane_list INTO r_plane. TRY. r_plane->display_attributes( ). CATCH lcx_list_error INTO r_exc.

Internal

exc_text = r_exc->get_exc_text( ). MESSAGE exc_text TYPE ’I’.

Only

exc_text = r_exc->previous->get_text( ). MESSAGE exc_text TYPE ’I’. ENDTRY. ENDLOOP. ENDMETHOD.

"display_airplanes

METHOD constructor. ... ENDMETHOD.

"constructor


08-03-2004


419


BC401

METHOD get_name. ... ENDMETHOD.

ENDCLASS.

"get_name


Use

Partner

Only

Internal

SAP

SAP Only

Internal

Use

Partner

420


08-03-2004

BC401


Lesson Summary

Only

Related Information

Use

Partner


Internal

You should now be able to: • Create exception classes • Trigger class-based exceptions in ABAP Objects programs • Propagate class-based exceptions in ABAP Objects programs • Handle class-based exceptions in ABAP Objects programs • Map class-based exceptions in ABAP Objects programs to each other

SAP

SAP Only

Internal

Use

Partner

08-03-2004


421


BC401

Lesson: Dynamic Programming with ABAP Objects for the SAP Web Application Server 6.20 Lesson Overview

Only Partner


Lesson Objectives

Use

Dynamically create objects Dynamically access class and object components Define field symbols Define data references Dereference data references Dynamically create data objects Ascertain the attributes of data objects at runtime

Partner

Business Example You want to add special dynamic programming techniques to your ABAP Objects implementations.

Field Symbols With field symbols, ABAP or ABAP Objects has offered dereferenced pointers for many releases. Field symbols allow you to access an assigned data object that is, all the accesses that you make to the field symbol are made to the

422


08-03-2004

Only

Internal

SAP

• • • • • • •

Use

As of SAP Web AS 6.10 at the latest, ABAP Objects objects offers at least the same possibilities that you may know from other programming languages. However, ABAP Objects stands out in the field of dynamic programming, particularly because ABAP Workbench supports it to such a high degree.

SAP

However, it is important for you to understand that this development took place, as it will help to explain why very similar concepts sometimes use quite different syntax structures.

Internal

Beginning with ABAP/4, the possibilities for dynamic programming with ABAP Objects have increased with the over several releases. This section will not retrace this development, it will give you a complete systematic introduction to the subject.

BC401

Lesson: Dynamic Programming with ABAP Objects for the SAP Web Application Server 6.20

data object assigned to it. Thus, you can only access the content of the data object to which the field symbol points. This is known as the “value semantics of field symbols”.

SAP

SAP

Use

Partner

Only

Internal

Figure 176: Field Symbols

Caution: Note that the parentheses () around the field symbol’s name are part of the syntax.

By specifying a type for the field symbol, you can ensure that only compatible objects are assigned to it.

For example: DATA: date TYPE d VALUE ’20040101’, time TYPE t. FIELD-SYMBOLS: TYPE d, TYPE t. ASSIGN: date TO , time TO . * possible? = .

08-03-2004


423

Only

Internal

You use the ASSIGN statement to assign a data object to a field symbol. If the field symbol is generically typed (TYPE ANY), it adopts the type of the object.

Partner

Use

You declare field symbols using the FIELD-SYMBOLS statement.


BC401

The last statement is a syntax error! Conversely, using the following construction would cause a runtime error: FIELD-SYMBOLS: TYPE ANY, TYPE ANY. Use the expression IS ASSIGNED to find out whether the field symbol is assigned to a field. The statement UNASSIGN sets the field symbol so that it points to nothing. The logical expression IS ASSIGNED is then false.

Use

Partner

Only

Internal

SAP

SAP

Use

If you use the CASTING TYPE addition when you assign a data object to a field symbol that has a different type, you can access the data object using the field symbol as if the object had the explicitly specified type. In the above example, note that the system field SY-DATUM is an elementary character-type component of length 8. You can also use type casting dynamically when you assign a data object to a field symbol.

424


08-03-2004

Only

Internal

If you use the CASTING addition when you assign a data object to a field symbol that has a different type, you can remove the restrictions of having to use the data object’s original type. The access is then interpreted as though the data object had the data type of the field symbol.

Partner

Figure 177: Type Casting with Field Symbols

BC401


For example: PARAMETERS tabname TYPE dd02l-tabname. DATA: dummy TYPE i, line(65535) TYPE c. FIELD-SYMBOLS TYPE ANY.

You can now access line using as if this elementary data object had the same type as the row type of the transparent table passed using tabname.

Partner

Note: You define the dummy data object only to ensure that line has the correct alignment.

Static and instance attributes can be accessed by assigning their contents to a field symbol. Syntactically, the attribute access takes the place of the data object.

Use

Attribute Access Using the ASSIGN Statement

SAP

SAP

Accessing Attributes Using Field Symbols

Internal

Only

ASSIGN line TO CASTING TYPE (tabname).

ASSIGN o_ref->instance_attribute TO .

You can also access it dynamically.

Dynamic Attribute Access Using the ASSIGN Statement DATA: classname

TYPE seoclsname VALUE ’CLASS’,

attributname TYPE seocpdname VALUE ’ATTRIBUTE’. ASSIGN (classname)=>(attributname) TO . ASSIGN o_ref->(attributname) TO .

08-03-2004


425

Only

Internal

If the field symbol has been typed generically, the missing type attributes are copied from the attributes during assignment.

Partner

Use

ASSIGN class=>static_attribute TO .


BC401

Data References In addition to field symbols, data and object references were also introduced to SAP R/3 4.6A in the transition to ABAP Objects. Since then, ABAP Objects contains complete reference semantics.

SAP

SAP

Use

Partner

Only

Internal

Note: The data syntax element represents a predefined name, comparable with space or constructor .

426


08-03-2004

Only

Internal

Data reference variables contain data references - that is, pointers to data objects. You can use the TYPE REF TO addition to the TYPES statement to define a reference type to a data object. You can specify the data type explicitly or choose the generic variation using TYPE REF TO data . In this case, your data reference can point to data objects of any type.

Partner

Use

Figure 178: Data References

BC401


You define the data reference variable itself using the DATA statement. This reference variable is a data object that can contain any data object (TYPE REF TO data) or a data object of the specified type. You work with data references using references. That is, when you access a data reference variable the data reference itself is accessed, so that changes are made to the addresses.

Only

You can also assign an existing data reference from another data reference variable or generate a data object dynamically using it. (This will be discussed in more detail later.)

SAP Use Internal

For example: DATA ref TYPE REF TO sflight. CREATE DATA ref.

08-03-2004


427

Only

If the data reference is statically typed as structured, you can also use the component selector -> to address the components of the referenced data object directly and use them in any operand position.

Partner

The expression data_reference->* is comparable to the expression .

SAP

Static references can be dereferenced directly using the dereferencing operator ->* ; this means they can access the content of the data object to which the reference points. For compatibility reasons, you must dereference generically typed data references (TYPE REF TO data) and assign them to a field symbol. You can then access their contents through the field symbol. (This will be explained in more detail later.)

Use

Partner

After it has been defined, the data reference variable is initial - that is, it contains an empty pointer. For a data reference variable to contain a reference that points to a data object, you must use the statement GET REFERENCE OF to obtain a reference to a data object that has already been defined.

Internal

Data references are handled in ABAP Objects like any data object with an elementary data type. This means that a reference variable can be defined not only as a single field, but also as the smallest indivisible unit in a complex data object, such as a structure or an internal table.


BC401

ref->fldate = ref->fldate + 5. WRITE: / ref->seatsmax.

Validity of References – Logical Expression ... ref IS [NOT] BOUND ...

The logical expression is true for a data reference if it can be dereferenced. The logical expression is true for an object reference if it points to an object. The logical expression is always false if ref contains the null reference.

SAP

Dynamic Instantiation and Calls

Use

Only

Internal

Partner

Syntax elements can be transferred dynamically for many statements. The syntax for doing this differs, depending on the statement you use:

SAP

In contrast, you can only use the expression ... ref IS [NOT] INITIAL ... to determine if ref contains the null reference or not.

Use

Partner

The expression ref IS [NOT] BOUND is used to query whether the reference variable ref contains a valid reference. ref must be a data or object reference variable.

Internal

Only

Here, the component selector is similar to the hyphen used with regular component access to structured data objects.

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Only

Internal

Figure 179: Dynamic Statements

SAP Use

For more information on which of these options you can use with a specific ABAP statement – if any – refer to the ABAP keyword documentation for that statement. In Open SQL statements, you can also specify the logical conditions of the WHERE clause dynamically at runtime, by entering the ABAP source code in a variable. In the FROM clause of the SELECT statement, you can specify either individual table names or a dynamic JOIN expression using a variable. Similarly, you can program the GROUP-BY and HAVING clauses in SELECT statements. For more information, refer to the ABAP keyword documentation. This principle also applies to the object-oriented statements in ABAP Objects. Using the following statement, you can instantiate objects dynamically:

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Only

Internal

Caution: Note: you must use upper case when filling data objects with literals.

Partner

For some statements, you can use a single-column internal table instead of one or more literals or identifiers.

SAP

If you pass the attribute as an identifier in the static form of the statement, you can replace the identifier with a variable in parentheses. Make sure there are no spaces between either parenthesis and the variable.

Use

If you pass the attribute as a literal in the static form of the statement, you can replace the literal with a variable.


BC401

Dynamic Instantiation of Objects DATA: classname TYPE seoclsname, o_ref TYPE REF TO object. ... CREATE OBJECT o_ref TYPE (classname) PARAMETER-TABLE it_par

The class name must be in the data object classname at runtime. The object reference o_ref must be compatible with this class or a common superclass, or it must be typed using TYPE REF TO object.

The current parameters and the return values of the exceptions must be passed dynamically using special internal tables. (This will be discussed in more detail later.) Instance methods are called dynamically according to the same principle:

SAP

SAP

Calling Instance Methods Dynamically CALL METHOD o_ref->(meth_name) PARAMETER-TABLE it_par

Use

Partner

EXCEPTION-TABLE it_exc.

or static methods

CALL METHOD (classname)=>(meth_name) PARAMETER-TABLE it_par EXCEPTION-TABLE it_exc.


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Internal

Calling Static Methods Dynamically

430

Use

Partner

Note: Compare to TYPE REF TO data.

Internal

Only

EXCEPTION-TABLE it_exc.

BC401


Partner

SAP

The table kind has three columns:

Partner

Use

The types ABAP_PARMBIND_TAB and ABAP_EXCPBINDTAB of both internal tables are defined globally in the ABAP type group. The parameter table must have the attributes of the ABAP_PARMBIND_TAB table kind.

Use

SAP

Only

Internal

Figure 180: Parameter Transfer and Exception Allocation for Dynamic Instantiations and Calls

NAME Name of the formal parameter

VALUE Value of the actual parameter (type: REF TO data) The way the parameter is passed is specified for each formal parameter in the declaration of the called method. Thus, the content of the KIND column can be initial. For the value of the actual parameter, the VALUE reference of the row in the table must point to the data object containing that value. You can use the GET REFERENCE statement to achieve this.

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Internal

KIND Type of parameter transfer (exporting, importing, changing, or receiving)


BC401

The exception table must have the attributes of the ABAP_EXCPBIND_TAB table kind. The table has two columns: NAME Name of exception VALUE Value for the return variable SY-SUBRC (type: I)

Only

Use

Partner

Internal

Caution: Exceptions can only be entered into the table according to the old concept. Alternatively, you can use the new class-based exception concept with implicit propagation (CX_NO_CHECK as the superclass), instead of the exception table.

SAP

SAP

In this example, the GET_MAKE method of the LCL_VEHICLE class is called dynamically. It has only one export parameter and no exceptions. First, define a parameter table called PTAB, with the global table kind ABAP_PARMBIND_TAB from the type group ABAP. The associated work area is called WA_PTAB. The WA_PTAB work area is filled with values: Assign the name of the export parameter EX_MAKE, to the component NAME. The component VALUE contains the reference to the corresponding actual parameter GD_MAKE. Also define the data reference

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Internal

Use

Partner

Figure 181: Dynamic Method Calls – Syntax Example

BC401


variable REF and fill the corresponding reference using GET REFERENCE. The KIND component of the work area does not need to be provided, as the runtime system gets the parameter type from the method’s signature. Then insert this work area in the parameter table PTAB using the INSERT statement. Finally, assign the name of the calling method to the data object METH. Then call the method using the syntax already shown.

Dynamic Instantiation and Cast Assignments for Data Objects

Partner

Using data references and the statement CREATE DATA, you can create data objects at runtime, as you can with class instances.

Use

Instantiation of Data Objects at Runtime DATA ref TYPE REF TO typename.

SAP

SAP

CREATE DATA ref.

Partner

Use

Then data reference ref then points to the created data object. As an alternative to the static variant, you can also set the data type at runtime.

Generic Typing of Data Objects at Runtime

CREATE DATA ref TYPE typename.

The reference ref must be generically-typed using TYPE REF TO data. The following dynamic variant shows how the type name typename can also be specified using a variable var_type:

Dynamic Instantiation of Data Objects at Runtime DATA ref TYPE REF TO data. DATA var_type TYPE ... . var_type = ... . CREATE DATA ref TYPE (var_type).


433

Only

Internal

DATA ref TYPE REF TO data.

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Internal

Only

After the method call, the actual parameter GD_MAKE contains the passed value.


BC401

To access the contents of this data object, you need to dereference the data reference first. For compatibility reasons, you need to use a field symbol if you are working with generically typed data references (TYPE REF TO data).

SAP

SAP

Use

Partner

Only

Internal

Figure 182: Dereferencing Generically Typed Data References

Use Internal

If the data reference is initial or invalid, it cannot be dereferenced. In that case the field symbol remains unchanged and SY-SUBRC is set to 4.

Generating Data Objects at Runtime – Application Example REPORT ... . DATA: ref_itab TYPE REF TO data,

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If the field symbol is fully generically typed, it adopts the type of the data object. If the field symbol is partially or completely typed, the system checks the compatibility of the data types. You can also cast to the assigned data object.

Partner

This statement ASSIGN ref_itab->* TO assigns the relevant data object (the one to which the data reference in the reference variable ref_itab points) to the field symbol . If the data object is assigned successfully, SY_SUBRC is set to 0.

BC401


ref_wa

TYPE REF TO data.

FIELD-SYMBOLS: TYPE ANY TABLE,

TYPE ANY,

TYPE ANY.

Internal

Only

PARAMETERS pa_tab TYPE dd02l-tabname DEFAULT ’SPFLI’. START-OF-SELECTION. CREATE DATA ref_itab TYPE STANDARD TABLE OF (pa_tab) WITH NON-UNIQUE DEFAULT KEY.

Partner

ASSIGN ref_itab->* TO . SELECT * FROM (pa_tab) INTO TABLE

Use

UP TO 100 ROWS. CREATE DATA ref_wa LIKE LINE OF . "or: TYPE (pa_tab).

SAP

SAP

ASSIGN ref_wa->* TO . LOOP AT INTO . DO. ASSIGN COMPONENT sy-index OF STRUCTURE TO . IF sy-subrc NE 0.

Partner

Use

NEW-LINE. EXIT. ENDIF. WRITE .

This example displays the content of a transparent table. You can make the FROM clause of the SELECT statement dynamic. For the INTO clause, you will need a data object that has a row type compatible with that of the table being displayed. Since the name – and thus the row type – of the table is not known until runtime, you should not create the data object until then. Unlike conventional data objects, you can dynamically specify the type of a data object created at runtime. The TYPE addition of the CREATE DATA statement contains the name of the table, so that the system creates the “appropriate” structure.

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Only

Internal

ENDDO. ENDLOOP.


BC401

The statement ASSIGN ref_wa->* TO assigns the data object to the field symbol. The data type of the table is inherited by the field symbol, so type casting is no longer necessary. You can now write each data record from the SELECT statement into the compatibly-typed data object using the field symbol .

Only

Use

Partner

Internal

If you knew the component names, you could display the fields directly using WRITE -.... However, you will not normally know the names of the components, nor how many of them there are. For this reason, you must display the components using the ASSIGN-COMPONENT variant: The components of the structure are assigned one-by-one to the field symbol and then displayed. When the loop runs out of components, the program requests the next data record.

SAP

SAP

Like object references, data references can be copied using cast operators in reference variables. However, the data reference’s static type must be the same as the dynamic type of the source reference. In this example, the first case meets this condition, the second does not. Note: Without the cast assignment operator ?=, these assignments would be impossible for syntactical reasons alone, because the source and target type are not compatible.

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Internal

Use

Partner

Figure 183: Cast Assignment for Data References

BC401


If a data reference variable has been typed statically, it passes on its type attributes whenever it is assigned to an untyped data reference. This is particularly advantageous for the additional information of global data types.

Use

Partner

Only

Internal

SAP Use

Only

Internal

Partner

During dereferencing, the type of reference variable, not data object, to which the reference “points” is the deciding factor. This will be demonstrated in the following example:

SAP

Figure 184: Copying Global Type Information for References – Principle

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437


BC401

SAP Use

Caution: This example has been set up intentionally to display that the type of a statically typed reference variable is actually the decisive factor.

Only

Internal

Hint: To get a more consistent result, the reference REF_CITYTO would have had to be typed either generically or in agreement with the data object CITYFROM.

Partner

438

SAP

In the example given here, the reference variable REF_CITYTO has been typed statically using a data element. At runtime, it contains a reference to the data object CITYFROM, which has been typed differently. The reference is then dereferenced through the generically typed field symbol , and it therefore adopts the type attributes of the reference. In this way, for example, the field documentation of the data element is listed during list output.

Use

Partner

Only

Internal

Figure 185: Copying Global Type Information for References – Syntax Example


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BC401


Type Analysis at Runtime Since the introduction of ABAP Objects, there is now a class-based concept called Run Time Type Information (RTTI), which you can use to find out type attributes at runtime. This concept includes all ABAP types, and so covers all of the functions of the now obsolete statements DESCRIBE FIELD and DESCRIBE TABLE. There is a description class for each type with special attributes for special type attributes:

Use

Partner

Only

Internal

Internal

To obtain a reference to a description object of a type, you must use the static methods of the class CL_ABAP_TYPEDESCR or the navigation methods of the special description class. The description objects are then created from one of the subclasses. At runtime, exactly one description object exists for each type. The attributes of the description object contain information on the attributes of the type.

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439

Only

The class hierarchy of the description classes corresponds to the hierarchy of the types in ABAP Objects. In addition, the description classes for complex types, references, classes, and interfaces have special methods used to specify references to sub-types. Using these methods, you can navigate through a compound type to all its sub-types.

Partner

Use

SAP

SAP

Figure 186: Dynamic Type Analysis for RTTI Classes


BC401

Dynamic Data Type Analysis – Application Example ... DATA: ref_descr TYPE REF TO cl_abap_structdescr, wa_comp

TYPE abap_compdescr.

...

Only

Internal

START-OF-SELECTION. ... * get reference to type descripion object by widening cast:

ref_descr ?= cl_abap_typedescr=>describe_by_data( ).

Use

Partner

...

TOP-OF-PAGE. LOOP AT ref_descr->components INTO wa_comp. WRITE wa_comp-name.

SAP Internal

Only the abstract class CL_ABAP_TYPEDESCR contains the method DESCRIBE_BY_DATA. Its RETURNING parameter is typed as a reference to this superclass. However, since the actual parameter REF_DESCR has the type of the subclass CL_ABAP_STRUCTDESCR, we need to assign the object using a widening cast. You can then access the attributes of the description instance in any form. In this example, the component names are displayed as the column headers. We have omitted the formatting options for the sake of clarity.

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Only

The functional method call returns the reference to the description instance of the structure. (The system creates the structure dynamically, which is why it is accessed through a field symbol).

Partner

Since we need the attributes of a structure, we first define a reference to the appropriate description class. Instances of this class possess a COMPONENTS attribute, which you use to describe the individual components of the relevant structure. This attribute is an internal table. Therefore you also need to define a work area with a compatible row type.

SAP

We can now enhance the application example of dynamic data object instantiation so that the system also displays the column names of the transparent table in the list.

Use

ENDLOOP.

BC401


Dynamic Object Type Analysis – Application Example CLASS lcl_rental IMPLEMENTATION. ... METHOD

add_vehicle.

*

only interested in busses - implemented using RTTI:

*

(alternative solution would be

*

using caught widening cast: ref_bus ?= sender)

Only

ref_class_descr ?= cl_abap_typedescr=>describe_by_object_ref( sender ). IF ref_class_descr->get_relative_name( ) = ’LCL_BUS’. ENDIF. ENDMETHOD.

"add_vehicle

...

SAP Use

The functional method call again returns the reference to the description instance of the vehicle instance. Only the abstract class CL_ABAP_TYPEDESCR owns the method DESCRIBE_BY_OBJECT_REF. Its returning parameter is typed as a reference to this superclass. However, since the actual parameter REF_CLASS_DESCR has the type of the subclass CL_ABAP_CLASSDESCR, we need to assign the object using a widening cast.

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Only

Internal

The reference to the triggering vehicle instance is mentioned in the SENDER parameter of the aforementioned event handler method. Its dynamic object type is to be analyzed to determine whether the vehicle in question is a bus or a truck.

Partner

We will now build upon this example: The vehicle rental company is now only interested in buses.

SAP

This application example is based on an example about event handling. In that simplified example, we specified that an instance of the vehicle rental class LCL_RENTAL reacts to an appropriate event by entering the vehicle instance that triggered the event into the list of owned vehicles, VEHICLE LIST. So far, the triggering instances could be buses (LCL_BUS) or trucks (LCL_TRUCK).

Use

Partner

APPEND sender TO vehicle_list.

Internal

DATA ref_class_descr TYPE REF TO cl_abap_classdescr.


BC401

You can then access the attributes of the description instance in any form. The functional method GET_RELATIVE_NAME supplies the class name. Note: You could also fulfill the same purpose without using RTTI classes: You could use a widening cast assignment from SENDER to a reference variable of static type LCL_BUS. That would cause a runtime error for an vehicle instances that are not buses. The system could then catch this runtime error. Not triggering a runtime error would therefore be the condition for entering a vehicle into the vehicle list.

Use

Partner

Only

Internal

SAP

SAP Only

Internal

Use

Partner

442


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Exercise 25: Type Casting with Data Elements (Optional) Exercise Objectives

Only

Business Example

Use

Partner

In the program for separating the character string into structured flight dates, the default value for the key date is to be calculated differently. The default value in the selection screen should now always be the first day of the next month.

Task 1: Copy the template.

SAP

Copy template: SAPBC401_TABS_PROCESS_DATA or ZBC401_##_PROCESS_DATA

SAP

1.

Program name: ZBC401_##_CASTING

Use

Partner

(Where ## is your two-digit group number). 2.

Activate your copy (or copies). Familiarize yourself with the program and its existing functions.

Define a suitable field symbol for structured access to an elementary date variable. 1.

Define a structure type (suggested name: ST_DATE) with three components: year, month, and day. Assign an appropriate type to each component.

2.

Define a field symbol based on this type (suggested name: ).



443

Only

Internal

Task 2:

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Internal

After completing this exercise, you will be able to: • Use field symbols to cast types • Calculate dates


BC401

Task 3:

Copy the date to the entry parameter PA_DATE.

2.

Assign the input parameter to the field symbol.

3.

Now fill the input parameter with the first day of the next month by using the field symbol to access the pseudo-components for the year, month, and day.

Use

Partner

1.

Internal

Only

Use the field symbol in the event block LOAD-OF-PROGRAM to calculate the default value.

SAP

SAP Only

Internal

Use

Partner

444


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Solution 25: Type Casting with Data Elements (Optional) Task 1: Copy the template. Copy template: SAPBC401_TABS_PROCESS_DATA or ZBC401_##_PROCESS_DATA Program name: ZBC401_##_CASTING (Where ## is your two-digit group number).

Partner SAP

Familiarize yourself with the program and its existing functions. a)


Define a structure type (suggested name: ST_DATE) with three components: year, month, and day. Assign an appropriate type to each component. a)

2.


Define a field symbol based on this type (suggested name: ). a)

Only

Internal

Define a suitable field symbol for structured access to an elementary date variable.


Task 3: Use the field symbol in the event block LOAD-OF-PROGRAM to calculate the default value. 1.

Copy the date to the entry parameter PA_DATE. a)


08-03-2004

Partner

1.

Activate your copy (or copies).

SAP

Task 2:

b)

Carry out this step in the usual manner. Additional information is available in the SAP Library. Model solution: SAPBC401_DYNS_CASTING

Use

2.

Use

a)

Internal

Only

1.


445


2.

BC401

Assign the input parameter to the field symbol. a)

3.


Now fill the input parameter with the first day of the next month by using the field symbol to access the pseudo-components for the year, month, and day. a)


Only

Internal


Partner

SAPBC401_DYNS_CASTING REPORT sapbc401_dyns_casting. TYPE-POOLS col.

Use

TYPES: BEGIN OF st_flight_c,

SAP

END OF st_flight,

SAP

Use

... END OF st_flight_c, BEGIN OF st_flight, ...

Partner

BEGIN OF st_date, year(4)

TYPE n,

Internal

month(2) TYPE n, day(2)

TYPE n,

END OF st_date.

Only

... FIELD-SYMBOLS TYPE st_date.

PARAMETERS: pa_date LIKE sy-datum, pa_alv

AS CHECKBOX DEFAULT ’X’.


446


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BC401


LOAD-OF-PROGRAM. pa_date = sy-datum. ASSIGN pa_date TO CASTING.

-day = ’01’. IF -month < 12. -month = -month + 1.

Internal

Only

ELSE. -month = ’01’. -year

= -year + 1.

Partner

ENDIF.

AT SELECTION-SCREEN. IF pa_date < sy-datum. " date in the past

Use

MESSAGE e085(bc401). ENDIF.

SAP

SAP

START-OF-SELECTION.

Only

Internal

Use

Partner

08-03-2004


447


BC401

Use

Partner

Only

Internal

SAP

SAP Only

Internal

Use

Partner

448


08-03-2004

BC401


Exercise 26: Creating Data Objects at Runtime Exercise Objectives

Only

Business Example

Hint: This program should help you to become familiar with the new programming techniques and to create an executable sample application. The Data Browser is already installed a standard tool for the ABAP Workbench.

Partner

SAP Use

Optimization of runtime requirements is not the focus of this exercise.

Task 1: Copy the template.

Internal

1.

Copy template: SAPBC401_DYNT_CREATE_DATA_SQL Program name: ZBC401_##_CREATE_DATA_SQL

Only

(Where ## is your two-digit group number). 2.

Activate your copy (or copies). Familiarize yourself with the program and its existing functions.


08-03-2004


SAP

Here, the user should only be able to select a table name. Filtering by field contents and other functions should be delegated to the SAP Grid Control, which should be used for outputting the data.

Use

Partner

You are to develop a program that can be used as an “ad-hoc data browser”.

Internal

After completing this exercise, you will be able to: • Dynamically instantiate data objects • Program dynamic Open SQL statements

449


BC401

Task 2:

Define a reference for the internal table that is to be generated (suggested name REF_ITAB).

2.

At program runtime, create a standard table with a non-unique default key. At this time, it is known which row type must be used.

3.

Assign a suitably-typed field symbol to the generated internal table so that its contents can be accessed (suggested name: ).

4.

Before calling the screen, program an Open SQL statement that copies data records from the selected database table into the internal table using an array fetch. If an error occurs, make sure the program terminates.

Task 3: Display the content of the internal table with an SAP Grid Control instance.

Use

Define a reference for the SAP Grid Control instance to be created (suggested name: REF_ALV).

2.

Within the PBO module INIT_CONTROLS_0100 already created, create an instance of the SAP Grid Control.

3.

Pass the filled internal table to this SAP Grid Control instance. If an error occurs, make sure that the program terminates. Hint: The relevant method is called SET_TABLE_FOR_FIRST_DISPLAY. It is sufficient to pass the row type to the parameter I_STRUCTURE_NAME and the name of the internal table to the parameter IT_OUTTAB.

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Only

Internal

Hint: The relevant class is called CL_GUI_ALV_GRID.

Partner

1.

SAP

SAP

Hint: For simplicity reasons, use the addition UP TO ... ROWS to limit the runtime requirements of the program. Later, you can program a more elegant solution for this.

Use

Partner

1.

Internal

Only

At runtime, create an internal table whose row type is compatible with the user’s selection. Import data from the selected transparent table into the internal table.

BC401


Solution 26: Creating Data Objects at Runtime Task 1: Copy the template. 1.

Copy template: SAPBC401_DYNT_CREATE_DATA_SQL

Only

(Where ## is your two-digit group number). Carry out this step in the usual manner. Additional information is available in the SAP Library. Model solution: SAPBC401_DYPS_CREATE_DATA_SQL 2.

Activate your copy (or copies). Familiarize yourself with the program and its existing functions. Carry out this step in the usual manner. Additional information is available in the SAP Library.

Task 2:

Use

1.

Define a reference for the internal table that is to be generated (suggested name REF_ITAB).

2.

At program runtime, create a standard table with a non-unique default key. At this time, it is known which row type must be used. a)

3.



Assign a suitably-typed field symbol to the generated internal table so that its contents can be accessed (suggested name: ). a)



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451

Only

Internal

a)

Partner

At runtime, create an internal table whose row type is compatible with the user’s selection. Import data from the selected transparent table into the internal table.

SAP

SAP

a)

Use

Partner

a)

Internal

Program name: ZBC401_##_CREATE_DATA_SQL


4.

BC401

Before calling the screen, program an Open SQL statement that copies data records from the selected database table into the internal table using an array fetch. If an error occurs, make sure the program terminates. Hint: For simplicity reasons, use the addition UP TO ... ROWS to limit the runtime requirements of the program. Later, you can program a more elegant solution for this.

Only


Task 3: 1.

Define a reference for the SAP Grid Control instance to be created (suggested name: REF_ALV).

Use

Partner

Display the content of the internal table with an SAP Grid Control instance.

Hint: The relevant class is called CL_GUI_ALV_GRID.

SAP

Within the PBO module INIT_CONTROLS_0100 already created, create an instance of the SAP Grid Control. a)


Pass the filled internal table to this SAP Grid Control instance. If an error occurs, make sure that the program terminates.

Internal

a)




452


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Only

Hint: The relevant method is called SET_TABLE_FOR_FIRST_DISPLAY. It is sufficient to pass the row type to the parameter I_STRUCTURE_NAME and the name of the internal table to the parameter IT_OUTTAB.

Partner

3.


SAP

2.

Use

a)

Internal

a)

BC401


SAPBC401_DYNS_CREATE_DATA_SQL REPORT

sapbc401_dyns_create_data_sql

.

DATA: ok_code LIKE sy-ucomm, popans.

Only

Internal

DATA: ref_docking TYPE REF TO cl_gui_docking_container, ref_alv TYPE REF TO cl_gui_alv_grid.

Partner

DATA ref_itab TYPE REF TO data.

FIELD-SYMBOLS TYPE ANY TABLE.

Use SAP

SAP

PARAMETERS pa_tab TYPE dd02l-tabname DEFAULT ’SPFLI’.

START-OF-SELECTION.

Use

Partner

CREATE DATA ref_itab TYPE STANDARD TABLE OF (pa_tab) WITH NON-UNIQUE DEFAULT KEY. ASSIGN ref_itab->* TO .

Internal

SELECT * FROM (pa_tab) INTO TABLE UP TO 100 ROWS. IF sy-subrc 0.

Only

MESSAGE a702(bc401). ENDIF.

CALL SCREEN 100.

*&---------------------------------------------------------------------*


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453


*&

Module

clear_ok_code

BC401

OUTPUT

*&---------------------------------------------------------------------* *

text

*----------------------------------------------------------------------* MODULE clear_ok_code OUTPUT. CLEAR ok_code. " clear_ok_code

OUTPUT

*&---------------------------------------------------------------------* *&

Module

STATUS_0100

OUTPUT

*&---------------------------------------------------------------------* *

text

Partner

*----------------------------------------------------------------------* MODULE status_0100 OUTPUT. SET PF-STATUS ’ST100’. ENDMODULE.

" STATUS_0100

Use

SET TITLEBAR ’T100’. OUTPUT

SAP

Module

init_controls_0100

OUTPUT

*&---------------------------------------------------------------------* *

text

SAP

*&---------------------------------------------------------------------* *&

Internal

Only

ENDMODULE.

Use

CREATE OBJECT ref_docking

Partner

MODULE init_controls_0100 OUTPUT.

Internal

*----------------------------------------------------------------------*

IF ref_docking IS INITIAL.

EXPORTING *

SIDE

= DOCK_AT_LEFT

Only

extension

= 2000

EXCEPTIONS OTHERS

= 6

. IF sy-subrc 0. MESSAGE a015(rfw). ENDIF.

CREATE OBJECT ref_alv


454


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BC401


EXPORTING i_parent

= ref_docking

EXCEPTIONS error_cntl_create = 1 error_cntl_init

= 2

error_cntl_link

= 3

error_dp_create

= 4

OTHERS

= 5

Internal

Only

. IF sy-subrc 0. MESSAGE a702(bc401).

Partner

ENDIF.

CALL METHOD ref_alv->set_table_for_first_display

i_structure_name

Use

EXPORTING = pa_tab

CHANGING it_outtab

=

SAP

SAP

EXCEPTIONS invalid_parameter_combination = 1 program_error

= 2

too_many_lines

= 3

OTHERS

= 4

Partner

Use

. IF sy-subrc 0. MESSAGE a702(bc401).

Internal

ENDIF.

ENDIF. " init_controls_0100

Only

ENDMODULE.

OUTPUT

*&---------------------------------------------------------------------* *&

Module

leave_programm

INPUT

*&---------------------------------------------------------------------* *

text

*----------------------------------------------------------------------* MODULE leave_programm INPUT. CLEAR popans.


08-03-2004


455


BC401

CALL FUNCTION ’POPUP_TO_CONFIRM_STEP’ EXPORTING textline1

= text-dml

textline2

= text-rcn

titel

= text-cnc

cancel_display = ’ ’ IMPORTING answer

= popans.

Internal

Only

CASE popans. WHEN ’J’. LEAVE PROGRAM. WHEN ’N’. CLEAR ok_code. " leave_programm

INPUT

*&---------------------------------------------------------------------* *&

Module

USER_COMMAND_0100

INPUT

*&---------------------------------------------------------------------*

SAP

text

*----------------------------------------------------------------------* MODULE user_command_0100 INPUT. CASE ok_code.

SAP

*

Use

Partner

ENDCASE. ENDMODULE.

WHEN ’BACK’.

Partner

Use

CLEAR popans. CALL FUNCTION ’POPUP_TO_CONFIRM_STEP’

Internal

EXPORTING textline1

= text-dml

textline2

= text-rbk

titel

= text-bak

cancel_display = ’ ’

Only

IMPORTING answer

= popans.

CASE popans. WHEN ’J’. LEAVE TO SCREEN 0. WHEN ’N’. ENDCASE. WHEN ’EXIT’.


456


08-03-2004

BC401


CLEAR popans. CALL FUNCTION ’POPUP_TO_CONFIRM_STEP’ EXPORTING textline1

= text-dml

textline2

= text-rex

titel

= text-ext

cancel_display = ’ ’ IMPORTING = popans.

Internal

Only

answer IF popans = ’J’. LEAVE PROGRAM. ENDIF.

Partner

WHEN OTHERS. ENDCASE. " USER_COMMAND_0100

INPUT

Use

ENDMODULE.

SAP

SAP

Flow Logic Screen 100 PROCESS BEFORE OUTPUT. MODULE clear_ok_code. MODULE status_0100.

Partner

Use

MODULE init_controls_0100.

PROCESS AFTER INPUT. MODULE leave_programm AT EXIT-COMMAND.

Only

Internal

MODULE user_command_0100.

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457


BC401

Lesson Summary

Only Partner

Related Information ... about this subject is available in the SAP Library and the ABAP keyword documentation for the individual statements.

Internal

You should now be able to: • Dynamically create objects • Dynamically access class and object components • Define field symbols • Define data references • Dereference data references • Dynamically create data objects • Ascertain the attributes of data objects at runtime

Use

SAP

SAP Only

Internal

Use

Partner

458


08-03-2004

BC401

Unit Summary

Unit Summary

Use

Only Partner

Internal

You should now be able to: • Create exception classes • Trigger class-based exceptions in ABAP Objects programs • Propagate class-based exceptions in ABAP Objects programs • Handle class-based exceptions in ABAP Objects programs • Map class-based exceptions in ABAP Objects programs to each other • Dynamically create objects • Dynamically access class and object components • Define field symbols • Define data references • Dereference data references • Dynamically create data objects • Ascertain the attributes of data objects at runtime

SAP

SAP Only

Internal

Use

Partner

08-03-2004


459

Unit Summary

BC401

Use

Partner

Only

Internal

SAP

SAP Only

Internal

Use

Partner

460


08-03-2004

BC401

Test Your Knowledge


The new exception concept replaces the old one. Thus, all old source code sections must be rewritten. As of SAP Web AS 6.20, function modules from the SAP standard system automatically raise object-oriented exceptions. Determine whether this statement is true or false.

Only

Unlike the old exceptions, those embodying the new concept can also be raised from subroutines and propagated. Determine whether this statement is true or false.

□ □ 3.

True False

The new exception classes can only be defined globally. This ensures central maintenance and reuse.

SAP

SAP

Determine whether this statement is true or false.

Internal

4.

True False

When you define an exception class, the superclass you choose specifies whether or not its exceptions must be caught explicitly with a TRY-CATCH-ENDTRY block and, if so, how the system reacts if the exception is not caught. Determine whether this statement is true or false.

08-03-2004

True False

Only

□ □

Partner

Use

□ □

Use

Partner

2.

True False

Internal

□ □


461

Test Your Knowledge

5.

BC401

Which of the following statements about dynamic programming are correct?

Partner SAP

D

□

E

□

F

□

G

□

H

□

I

□

J

□

K

Internal

Use

□

462


08-03-2004

Only

C

Partner

□

Field symbols contain addresses of data objects at runtime. If you change the contents of a field symbol, you also change the address of the assigned data object. If you change the contents of a field symbol, you consequently change an address. That is, the field symbol then does not point to the data object anymore. You can use field symbols to access data objects as if their type was not static. There are no data references in ABAP Objects. Instead, there are only dereferenced pointers with field symbols. If you change the contents of an assigned data reference, you consequently change an address. That is, the reference then does not point to the data object anymore. In ABAP Objects, you can set the type of an object when you define the reference or you can do it later when the generation takes place at runtime. In ABAP Objects, you can set the type of a data object during the definition or you can do it later when the generation takes place at runtime. A globally typed data reference points to a data object that was typed with a different global type. Furthermore, the data reference is dereferenced using a generically typed field symbol. If this field symbol is then used to access the data object, the type attributes of the data object, not the data reference, take effect. If a data reference variable has been typed statically, it passes on its type attributes whenever it is assigned to an untyped data reference. RTTI classes can be used in ABAP Objects to specify all type attributes of a (data) object at runtime.

SAP

A B

Use

□ □

Internal

Only


BC401

Test Your Knowledge

Answers 1.

The new exception concept replaces the old one. Thus, all old source code sections must be rewritten. As of SAP Web AS 6.20, function modules from the SAP standard system automatically raise object-oriented exceptions.

Refer to the relevant section of the lesson. Unlike the old exceptions, those embodying the new concept can also be raised from subroutines and propagated. Answer: True Refer to the relevant section of the lesson. The new exception classes can only be defined globally. This ensures central maintenance and reuse.

SAP

SAP

3.

Answer: False Refer to the relevant section of the lesson.

Use

Answer: True Refer to the relevant section of the lesson. 5.

Which of the following statements about dynamic programming are correct? Answer: A, D, F, G, H, J, K Refer to the relevant section of the lesson.

08-03-2004


463

Only

Internal

When you define an exception class, the superclass you choose specifies whether or not its exceptions must be caught explicitly with a TRY-CATCH-ENDTRY block and, if so, how the system reacts if the exception is not caught.

Partner

4.

Use

Partner

2.

Internal

Only

Answer: False

Course Summary

BC401

Course Summary You should now be able to: •

Use

Partner

• • •

Internal

Only

• • •

Name and use the syntax elements for Unicode-compatible character string processing Use internal tables to optimum effect Use fundamental elements of object-oriented modeling in UML Create ABAP Objects programs that contain all useful object-oriented programming techniques Use the relevant tools to create object-oriented Repository objects Define, raise, and handle class-based exceptions Name and use the syntax elements for dynamic programming

SAP

SAP Only

Internal

Use

Partner

464


08-03-2004

Appendix 1 Calling Programs and Passing Data

In ABAP Objects, there are two main ways of starting programs from within other programs:

SAP

Restart The current program is terminated and the called program is started.

SAP

Background Information The flow of the calling program is interrupted while the called program runs and is then continued after the called program has finished.

Use

Partner

Only

Internal

Calling Programs

Only

Internal

Use

Partner

Figure 187: Calling Programs

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465


BC401

Complete programs within a single user session can run only sequentially. We refer to this technique as sequential calling. If you want to run activities in parallel, you must use function modules. Note: More information about this technique is available in other courses and the ABAP keyword documentation for the statement CALL FUNCTION ... STARTING NEW TASK ... .

Use

Partner

Only

Internal

SAP

SAP

Use

If you use the AND RETURN addition, the system resumes processing with the first statement after the SUBMIT statement, once the called program has finished. Note: For further information, refer to the ABAP keyword documentation for the SUBMIT statement.

466


08-03-2004

Only

Internal

To start an executable program, use the SUBMIT statement. If you use the VIA SELECTION-SCREEN addition, the system displays the standard selection screen of the program (if one has been defined).

Partner

Figure 188: Calling an Executable Program

BC401


Use

Partner

Only

Internal

Figure 189: Calling a Transaction

SAP Use

To force the termination of a program, use the LEAVE PROGRAM statement. If the statement is used in a program that you called using CALL TRANSACTION ’T_CODE’ or SUBMIT prog_name AND RETURN , the system resumes processing at the next statement after the call in the calling program. Otherwise, the user returns to the application menu from which he or she started the program. If you use the ... AND SKIP FIRST SCREEN addition, the system does not display the screen contents of the first screen in the transaction.

08-03-2004


467

Only

Internal

The statement CALL TRANSACTION ’T_CODE’ allows you to insert ABAP programs that have a transaction code.

Partner

LEAVE TO TRANSACTION ’T_CODE’ statement you terminate the current program and start the transaction with the transaction code T_CODE. The statement is the equivalent to entering /nT_CODE in the command field.

SAP

With the


BC401

Caution: The flow logic is processed. If the transaction you called with CALL TRANSACTION ’T_CODE’ uses update techniques, you can use the UPDATE ... addition to specify the update technique (asynchronous (default), synchronous, or local) that the program should use.

Only

Management of Working Memory

Use

Partner

The way in which the working memory is organized from the program’s point of view can be represented easily using a model.

Internal

Note: For further information, refer to the course BC414 (Programming Database Updates) and the SAP Library.

SAP

SAP Only

Internal

Use

Partner

Figure 190: Logical Memory Model

468


08-03-2004

BC401


There is a distinction between internal and external sessions: •

Data for a program is only visible within an internal session. In general, data visibility is restricted to the relevant program.

Partner

The following illustrates how the stack inside an external session changes with various program calls. The starting situation for the first case is the execution of the statement SUBMIT ... AND RETURN or CALL TRANSACTION within a program.

Internal

Only

•

Generally, an external session is connected to an SAP Web AS window. The session can be opened with System → New session or by entering /oT_CODE in the command field. You can have up to six external sessions open simultaneously in one terminal session. External sessions are subdivided into internal sessions (placed on a stack). Each program that you run occupies its own internal session. Each external session can contain up to nine internal sessions.

Use

SAP

SAP Only

Internal

Use

Partner

Figure 191: Inserting a Program -1

08-03-2004


469


BC401

Use

Partner

Only

Internal

Figure 192: Inserting a Program -2

SAP

SAP

When you insert a program, the system creates a new internal session, which in turn creates a new program context. The new session is placed on the stack. The program context of the calling program therefore remains intact.

Only

Internal

Use

Partner

Figure 193: Terminating the Inserted Program

470


08-03-2004

BC401


When the called (inserted) program finishes, its internal session (the top one in the stack) is deleted. Processing is resumed in the next-highest internal session in the stack. When you end a program and start a new one, there is a distinction between calling an executable program and calling a transaction, with regard to memory areas. The starting situation for the second case is therefore the execution of the statement SUBMIT within a program.

Use

Partner

Only

Internal Partner

Use

SAP

SAP Only

Internal

Figure 194: Restarting an Executable Program -1

08-03-2004


471


BC401

Use

Partner

Only

Internal

SAP

Only

Internal

Partner

The starting situation for the third case is therefore the execution of the statement LEAVE TO TRANSACTION within a program.

SAP

If you call an executable program using its program name (terminating the calling program), the system deletes the internal session of the program that you are terminating (the top one from the stack). The system creates a new internal session, which in turn creates the program context of the called program. The new session is placed on the stack. Existing program contexts remain intact. The topmost internal session on the stack is replaced.

Use

Figure 195: Restarting an Executable Program -2

472


08-03-2004

BC401


Use

Partner

Only

Internal

Figure 196: Restarting a Transaction -1

SAP

SAP Only

Internal

Use

Partner

Figure 197: Restarting a Transaction -2

If you start a program using its transaction code (if one was defined), all of the internal sessions on the stack are deleted. The system creates a new internal session, which in turn creates the program context of the called program.

08-03-2004


473


BC401

Caution: Therefore, the ABAP memory is also initialized after the call.

Data Transfer There are various ways of passing data to programs running in separate internal sessions. However, we are only dealing with those that are platform-independent and only exchange data transiently.

Use

Partner

Only

Internal

• • • • •

The interface of the called program (usually a standard selection screen) ABAP memory SAP Memory Database tables Local files on your presentation server

The following only introduces the first three techniques, because only these meet the specified requirements.

474


08-03-2004

Only

Internal

You can use the following techniques to pass data:

Partner

Use

SAP

SAP

Figure 198: Passing Data Between Programs – Overview

BC401


Figure 199: Passing Data Using the Program Interface

• •

By specifying a variant for the selection screen when you call the program When the program is called, you predefine specific values for the input fields

Use

Partner

When you call ABAP programs that have a standard selection screen, you can pass data for the input fields in the call. There are two ways to do this:

Internal

Only

For further information about passing data using database tables or the shared buffer, refer to the ABAP keyword documentation for the EXPORT and IMPORT statements. For further information about transferring data between an ABAP program and your presentation server, refer to the documentation for the function modules GUI_UPLOAD and GUI_DOWNLOAD.

SAP

SAP Only

Internal

Use

Partner

Figure 200: Preassigning Values for Input Fields

The WITH addition to the SUBMIT statement allows you to preassign values for parameters and selection options on a standard selection screen of the called executable program. The relational operators EQ, NE, ... and the inclusion operators I and E have the same meanings as with select-options.

08-03-2004


475


BC401

If you want to predefine several selections for a selection option, you can use the RANGE statement instead of individual WITH additions. The RANGES statement creates a selection table, which you can fill as though it were a selection option. You then pass the whole table to the executable program. If you want to display the standard selection screen when you call the program, use the VIA SELECTION-SCREEN addition.

Only

Use

Partner

For further information about working with variants and other syntax variants of the WITH addition, refer to the ABAP keyword documentation for the SUBMIT statement.

Internal

In the ABAP Editor, use the statement pattern to insert a program call using SUBMIT. The pattern supplies the names of the parameters and selection options that are available on the standard selection screen.

SAP

SAP

Internal

Use

Partner

476


Only

Figure 201: ABAP Memory and SAP Memory

08-03-2004

BC401


You can use the SAP Memory and the ABAP memory to pass data between programs: •

SAP Memory is a user-specific memory area for storing field values. It is therefore of limited use when passing data between internal sessions. Values in SAP Memory are retained for the duration of the user’s terminal session. The memory can be used between sessions in the same terminal session. All external sessions can access SAP Memory.

Only

ABAP memory is also user-specific. There is a local ABAP memory for each external session. You can use it to exchange any ABAP data objects (fields, structures, internal tables, complex objects) between the internal sessions in any one external session. When the user exits an external session (/i in the command field), the corresponding ABAP memory is automatically initialized or released.

Use

Partner

•

Internal

You can use the contents of SAP Memory as default values for screen fields.

SAP

SAP Only

Internal

Use

Partner

Figure 202: Passing Data Using the ABAP Memory

Use the EXPORT ... TO MEMORY statement to copy any number of ABAP variables with their current values (data cluster) to the ABAP memory. The ID... addition (maximum 32 characters long) enables you to identify different clusters.

08-03-2004


477


BC401

If you use a new EXPORT TO MEMORY statement for an existing data cluster, the new one will overwrite the old. The IMPORT ... FROM MEMORY ID ... statement allows you to copy data from the ABAP memory into the corresponding fields of your ABAP program.

To release a data cluster, use the FREE MEMORY ID ... statement.

Use

Partner

Caution: Remember when you call programs using transaction codes that you can use the ABAP memory to pass data to the transaction only when calling it (CALL TRANSACTION).

Internal

Only

In the IMPORT statement, you can also restrict the selection to a part of the data cluster. The variables into which you want to read data from the cluster in the ABAP memory must have the same types in both the exporting and the importing programs.

SAP

SAP

Internal

Use

Partner

Figure 203: Passing Parameters Using the SAP Memory

Only

478


08-03-2004

BC401


You can define memory areas (parameters) in the SAP Memory in various ways: •

By creating input/output fields with reference to the ABAP Dictionary. These adopt the parameter name of the data element to which they refer. Alternatively, you can enter a name in the attributes of the input/output fields.

Only

To find out about the names of the parameters assigned to input fields, display the input help (F4) for the field, and choose Technical info.

SAP

SAP

•

You can also fill a memory area directly using the statement SET PARAMETER ID ’PAR_ID’ FIELD var. then read it using GET PARAMETER ID ’PAR_ID’ FIELD var. . Finally, you can define parameters in the Object Navigator and let the user fill them with values.

Use

Partner

•

Internal

Here, you can also choose whether the entries from the field should be transferred to the parameter (SET), or whether the input field should be filled with the value from the parameter (GET).

Only

Internal

Use

Partner

Figure 204: Passing Data Using an Internal Table – Preview

08-03-2004


479


BC401

When you call a transaction using the statement CALL TRANSACTION ’T_CODE’ USING bi_itab, you can run the transaction T_CODE using the values from bi_itab in the screen fields. The internal table must have the structure BDCDATA and be filled accordingly.

You can use the MESSAGES INTO statement to specify an internal table into which any system messages should be written. The internal table must be typed according to the structure BDCMSGCOLL.

This technique is useful if, for example: •

SAP

SAP

•

You are processing in the foreground, but the input fields have not been filled using GET parameters You want to process the transaction in the background. In this case, you normally have to pass function codes as well.

Use

Partner

You can find out if the transaction was executed successfully from the return value SY-SUBRC.

Internal

Only

The MODE addition allows you to specify whether the screen contents should all be displayed (A - the default setting), only displayed when an error occurs (E), or not displayed at all (N).

Internal

Use

Partner

480


Only

Figure 205: Fields of the Global Type BDCDATA

08-03-2004

BC401


Filling the internal table in “batch input format”: •

•

Each screen that is to be processed and filled automatically in the transaction must be identified by a row in which only the fields PROGRAM, DYNPRO, and DYNBEGIN are filled. After the record that identifies the screen, use a separate BDCDATA record for each field you want to fill. These records use the table fields FNAM and FVAL. You can fill the following fields:

Only

Input/output fields (with data) The command field BDC_OKCODE (with a function code) The cursor positioning field, BDC_CURSOR (with a field name)

For further information, refer to the course BC420 (Data Transfer) and the SAP Library.

Use

Partner

This technique is also one of the possible ways of transferring data from non-SAP systems. To do so, the internal table in the BDCDATA format must be filled completely.

Internal

– – –

SAP

SAP Only

Internal

Use

Partner

Figure 206: Passing Data Using an Internal Table – Application Example

The above example refers to the example transaction BC401_CALD_CTA_U in package BC401. When the user creates a new customer entry, the program calls transaction BC401_CALD_CRE_CUST. This transaction has

08-03-2004


481


BC401

not implemented an import from the ABAP memory, and its input fields are not set as GET parameters. The customer data is therefore passed using an internal table and the transaction is processed in the background. If the operation is successful, the new customer data record can be entered in the waiting list. The filled internal table in BDCDATA format is illustrated above.

Only

Use

Partner

Internal

At runtime, CURRENT_NAME stands for the customer name adopted from the input field, CURRENT_CITY stands for the city. You address the command field using BDC_OKCODE. Here you enter the function code that is triggered by the user choosing a function key, pushbutton, or menu entry during the dialog flow (or by entering a code directly in the command field).

SAP

SAP Only

Internal

Use

Partner

482


08-03-2004

Index Only SAP Use Internal

08-03-2004


483

Only

basis class, 371 BINARY SEARCH, 47

CA, 6 CALL METHOD, 139–140 EXCEPTION-TABLE, 429 EXCEPTIONS, 129 EXPORTING, 128 IMPORTING, 128 PARAMETER-TABLE, 429–430 calling methods dynamically, 430 cardinality, 112 cast assignment operator, 436 CATCH, 386 CHANGING, 128 character length, 3, 5 character representation internal, 3 character set table, 3 character-type, 5 class, 106, 121 abstract, 352 CL_ABAP_CHAR_UTILITIES, 5

Partner

B

C

SAP

abstraction, 108 ACTIVATION, 269 aggregation, 113, 137 alias name, 230, 238 ALIASES, 230 alignment, 7 alignment gap, 7 alignment requirement, 7 APPEND, 30–31, 39 SORTED BY, 31 ASCII character set, 3 ASSIGN, 423, 434 CASTING, 424 CASTING TYPE, 424 association, 112 binary, 112 recursive, 112 AT NEW, 37, 42 attribute, 122 AGENT, 371 KERNEL_ERRID, 386 PREVIOUS, 397 private, 124 public, 124 static, 126

Use

Partner

A

byte sequence processing, 4–5 BYTE-CA, 7 BYTE-CN, 7 BYTE-CO, 7 BYTE-CS, 7 BYTE-NA, 7 BYTE-NS, 7 byte-type, 5

Internal

Numerics/Symbols ~, 229–230 ?=, 200, 235, 436 [], 38 ->*, 427, 434

Index

BC401

Only Partner SAP Use Internal

Only

08-03-2004

Partner

DATA TYPE REF TO, 134, 427, 437 TYPE REF TO data, 427 data reference variables, 426 data references, 426 data type table-type, 23 database management system object-oriented, 370 DEFAULT, 128 DEFAULT KEY, 26 DEFINITION, 122 definition part, 122 delegation, 115 delegation principle, 102 DELETE, 32, 34

SAP


D

Use

484

CN, 6 CO, 6 COLLECT, 30 ASSIGNING, 43 REFERENCE INTO, 43 COMMIT WORK, 371 component interface, 237 composition, 113 compound interface, 237 constructor, 144, 191 static, 146 CONSTRUCTOR, 144 container control, 326 control level processing, 37, 42 CP, 6 CREATE DATA, 433 TYPE, 433 CREATE OBJECT, 135 TYPE, 429 CS, 6

Internal

CL_ABAP_CLASSDESCR, 441 CL_ABAP_STRUCTDESCR, 440 CL_ABAP_TYPEDESCR, 439–441 CL_GUI_ALV_GRID, 326 CL_GUI_CUSTOM_CONTAINER, 326 definition part, 122 final, 353 friendship, 355 instantiation, 354 persistent, 370 CLASS, 121, 307 ABSTRACT, 352 CREATE, 354 DEFINITION, 121 FINAL, 353 FRIENDS, 355 INHERITING FROM, 188 PRIVATE SECTION, 125 PUBLIC SECTION, 125 class actor, 371 class agent, 371 class attribute, 126 Class Builder display settings, 319 editing class components, 313 class diagram, 111 CLASS EVENTS, 266 class method, 131 CLASS_CONSTRUCTOR, 146 CLASS-METHODS, 131 classes without multiple instantiation, 357 CLEANUP, 387, 392 CLEAR, 33

BC401

Index

G Garbage Collector, 136 generalization, 113, 186 global class


485

Only SAP Use Internal

Only

field symbol, 422 FIELD-SYMBOLS, 423 fragment view, 7 FREE, 33 friend concept, 355 friendship relationship, 355 inheritance, 356 function CHARLEN, 5 STRLEN, 6 XSTRLEN, 6 function group data management, 96

Partner

08-03-2004

F

SAP

encapsulation, 96, 124 ENDAT, 37, 42 ENDTRY, 386 Enjoy Demo Center, 328 event static, 263 event handler method, 264 event-controlling, 103 EVENTS, 266 exception, 383 class-based, 383 mapping, 397–398 propagate, 386, 390 exception chain, 384, 397 exception class CX_DYNAMIC_CHECK, 385, 396 CX_NO_CHECK, 385, 396, 432 CX_OS_OBJECT_EXISTING, 371 CX_OS_OBJECT_NOT_FOUND, 372 CX_ROOT, 385, 397 CX_STATIC_CHECK, 385, 396

Use

Partner

E

CX_SY_ARITHMETIC_ERROR, 388 CX_SY_ARITHMETIC_OVERFLOW, 387 CX_SY_MOVE_CAST_ERROR, 202, 235 CX_SY_ZERODIVIDE, 386 global, 384 inheritance hierarchy, 396 local, 384 superclass, 396 Exception class, 384 exception handling, 384, 386 static check, 396 syntax check, 396 exception instance, 384 exception texts multiple, 385 EXPORT TO DATA BUFFER, 5

Internal

ADJACENT DUPLICATES FROM, 32 TRANSPORTING, 32 WHERE, 32 dereferencing, 427, 434, 437–438 dereferencing operator, 427, 434, 437 DESCRIBE FIELD, 439 LENGTH, 6 DESCRIBE TABLE, 439 destructor, 145 downcast, 200, 235

Index

BC401

print, 313 test, 314

H

Only

I

LOOP AT, 36–37 ASSIGNING, 42, 48 REFERENCE INTO, 43, 48 TRANSPORTING NO FIELDS, 37 WHERE, 47

M ME, 147 MESSAGE, 388 method, 128

08-03-2004

Only

Partner SAP Use Internal

L

Partner


KEY, 26

SAP

486

K

Use

IMPORT FROM DATA BUFFER, 5 IN BYTE MODE, 6 IN CHARACTER MODE, 5 indicator OO transaction model, 329 information hiding, 124 inheritance, 103 INITIAL SIZE, 28, 32 INSERT, 30–31 ASSIGNING, 43 REFERENCE INTO, 43 instance, 107 instance attribute, 126 instance constructor, 144, 191 visibility section, 354 instance event, 263 instance method, 131 instantiating objects dynamically, 429 instantiation class, 133 data type, 433 interface class, 124 compound, 237 method, 128 INTERFACE, 229 interface resolution operator, 229–230

Internal

handler table, 270 hash algorithm, 45 hash function, 45 hashed table, 24, 45, 52 HASHED TABLE, 25 header line, 38

INTERFACES, 229 internal table attributes, 23 column, 22 control level processing, 37, 42 data type, 23 entry, 22 hash, 24 hash management, 45 header line, 38 index access, 23 initial size, 28 key, 23 key access, 23 row type, 23 sorted, 24 standard, 24 standard key, 26 standard type, 26 table kind, 23 table scan, 47 unstructured row type, 26, 44 IS ASSIGNED, 424 IS BOUND, 428 IS INITIAL, 428

BC401

Index

Only Partner SAP

object, 106 behavior, 110 identity, 107 persistent, 370 status, 107, 110 Object GUID, 370 object link, 112 Object Management Group (OMG), 109 offset access, 9–10 OO transaction, 328 Open SQL statement dynamic, 429 OPTIONAL, 128

P


487

Only

package, 110 Persistence Service, 370 persistent, 369 pointer dereferenced, 422 polymorphism, 103, 199, 233 prefix BYTE-, 7 PRIVATE SECTION, 125 processing character strings, 4–5 programming model object-oriented, 100 procedural, 95 PROTECTED SECTION, 192 PUBLIC SECTION, 125

Partner

Use

O

SAP

Internal

NA, 6 namespace class, 130 narrowing cast, 195, 232 NON-UNIQUE, 25 NP, 6 NS, 6 null reference, 134, 428

Use

08-03-2004

N

Internal

abstract, 352 call, 139–140 CREATE_PERSISTENT, 371 DESCRIBE_BY_DATA, 440 DESCRIBE_BY_OBJECT_REF, 441 final, 353 functional, 141 GET_PERSISTENT, 372 GET_RELATIVE_NAME, 442 GET_SOURCE_POSITION, 385 GET_TEXT, 385, 387, 390, 392 private, 130 public, 130 redefinition, 189 REFRESH_TABLE_DISPLAY, 328 SET_TABLE_FOR_FIRST_DISPLAY, 327 signature, 128 static, 131, 353 METHODS, 131 ABSTRACT, 352 FINAL, 353 FOR EVENT, 267 MODIFY, 32, 34 ASSIGNING, 43 REFERENCE INTO, 43 TRANSPORTING, 32 WHERE, 32 MOVE, 135 ?TO, 200, 235, 436 multiple inheritance, 188 multiple instantiation, 100 multiplicity, 112

Index

BC401

R

08-03-2004

Only Partner SAP Use Internal

Only


Partner

488

table scan, 47 TABLE_LINE, 26, 44, 136 text ID, 391 transaction code, 328 transaction service, 328 transient, 369 TRY, 386 type ABAP_EXCPBIND_TAB, 431 ABAP_PARMBIND_TAB, 431 dynamic, 195 static, 195 TYPE REF TO, 134 TYPE REF TO data, 426

SAP

SAP Control Framework, 324 SAP Grid Control, 325 Self-Reference, 147 SENDER, 267 sequence diagram, 114 SET HANDLER, 269 ACTIVATION, 269

T

Use

S

FOR ALL INSTANCES, 269 signature, 128 singleton, 357 singleton class, 357 SORT, 34 SORTED BY, 31 sorted table, 24, 51 SORTED TABLE, 25 specialization, 113, 185–186 standard key, 26 standard table, 24, 51 STANDARD TABLE, 25 static attribute, 126 static constructor, 146 static method, 131 subclass, 185–186 SUPER, 189 superclass, 185–186 syntax check Unicode check, 4 system field SY-TABIX, 35, 37 SY-TFILL, 35 SY-TLENG, 35

Internal

RAISE EVENT, 267 RAISING, 391 READ TABLE, 35–36 ASSIGNING, 42, 48 BINARY SEARCH, 47 COMPARING, 35 REFERENCE INTO, 43, 48 TRANSPORTING, 36 TRANSPORTING NO FIELDS, 36 READ-ONLY, 123, 125 redefinition, 189 Refactoring Assistant, 322 reference independent, 136 validity, 428 reference semantics, 427 reference types, 437 reference variable, 134, 426 data type, 437 REFRESH, 33 registration, 268, 270 RETURNING, 128 role, 112 role design pattern, 204 RTTI, 439 runtime error BCD_ZERODIVIDE, 386 catchable, 384 Runtime Type Identification (RTTI), 439

TYPE REF TO object, 430 TYPES TYPE REF TO, 426, 437 TYPE REF TO data, 426

V

U

W

UML, 109 UNASSIGN, 424 Unicode, 3 fragment view, 7 Unified Modeling Language, 109 UNIQUE, 25 upcast, 195, 232

widening cast, 200, 235 widening cast assignment operator, 200, 235 WITH, 25 DEFAULT KEY, 26 WITH HEADER LINE, 38

value semantics, 423 visibility section protected, 192

Use

Partner

Index

Internal

Only

BC401

SAP

SAP Only

Internal

Use

Partner

08-03-2004


489

Index

BC401

Use

Partner

Only

Internal

SAP

SAP Only

Internal

Use

Partner

490


08-03-2004

Feedback Only

Use

Partner

Internal

SAP AG has made every effort in the preparation of this course to ensure the accuracy and completeness of the materials. If you have any corrections or suggestions for improvement, please record them in the appropriate place in the course evaluation.

SAP

SAP Only

Internal

Use

Partner

08-03-2004


491

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