chapter 01_fundamentals of abap object

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© Copyright IBM Corporation 2007

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Fundamentals of ABAP Objects



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© 2007 IBM Corporation2 Jan-2007Fundamentals of ABAP Objects

Objectives

Upon completion of this chapter, the participants will be able to: Recognize the concept of Object Oriented Programming (OOP)

Identify the features of Object Oriented Programming & its Advantages

Recall the history of ABAP Object Oriented Programming

Identify the need to learn ABAP Objects

Analyze the basic building blocks of ABAP Objects

Create a local Class with Attributes, Methods, Constructors.



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Features of Procedural Programming Model

Data and Functions are kept separate. Global variables of program contains data,while subroutine contains functions.

Usually non-encapsulated access to data. (exception: Global data of Function

Group is only accessible by Function Modules within that group).

Program maintenance as well as management becomes difficult as program size

increases. Very difficult to model real word entity.

Not possible to create several runtime instances easily.

Data

Data

Data

Function

Function

Function



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What is Object Oriented Programming (OOP) ?

The fundamental idea behind Object Oriented Programming (OOP) is to combine both data and the functions (methods) those operate on that data into a single

unit. Such an unit is called Object.

Possibility of creating several runtime instances is one of the key characteristics

of Object Oriented Programming. This allows you to create a direct abstraction of

a real world object.

Data

Function

Object



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Basic building blocks of OOP

Classes and Objects are the basic building blocks of Object OrientedProgramming. When a real world entity is modeled into OOP world then it is

known as Class, characteristics as attributes and functionality as methods.

Objects are instances of a Class.

Example :

What are the

characteristics of the

box? (Attributes)

Inside color is blue

(Private)

Outside color is

white (Public)

What is the status of the box ? (Events)

The box is semi open

Functions of the box? (Methods)

It can store things

It can occupy space



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Client/Server Relationship & Delegation

Objects behave like Client/Server systems.

When an objects sends a message to another object, telling it to behave in a

particular way, the first object can be seen as a Client and the second as a Server

In OOP services are distributed among objects to avoid redundancy and each

object offers only those services that are within its area of responsibility.

If an object needs any other services, it requests these from other objects. This isknown as principle of delegation.

Data

Object 1

Data

Object 2

Sends Message toRetrieve Details

Function:

GET_DETAILS

Function:

RETRIEVE_DETAILS



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Features of Object Oriented Programming

Abstraction Modeling real world entities and processes in a more natural way.

Ecapsulation

Hiding data and its related logic behind well defined interfaces.

Inheritance

Reusing attributes and methods while allowing for specialization.

Polymorphism

Simplifying by hiding varying implementations behind the same interface.

Code Reuse

Same code can be reused multiple times by using inheritance.



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Advantages of Object Oriented Programming

Real world entity can be modeled very well.

Provides advance level of data encapsulation that improves the maintainability

and stability of ABAP programs.

Better programming structure, reduced maintenance effort & less susceptibility to

errors.

Software extension is simpler & more secure.

Stress on data security and access.

Data encapsulation and abstraction.

Once a base class is written and tested, it need not be touched again. Reusing

existing code through “Inheritance” saves time, money and increase a programs

reliability.



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History of ABAP Object Oriented Programming

Object Oriented Programming (OOP) in general was developed at approximatelythe same time as procedural programming models.

In SAP:

SAP Basis Release 4.5 delivered the first version of ABAP Objects.

SAP Basis Release 4.6 delivered complete version of ABAP Objects by introducing

‘Inheritance’. SAP Web Application Server 6.10/6.20 enhanced ABAP Objects with Friendship and

Object Services.

The object-oriented concept in ABAP is same as other modern object-oriented

languages such as C++ or Java.



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ABAP as Hybrid Language

The ABAP runtimesupport for both theprocedural and ABAPObjects programmingmodels



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ABAP as Hybrid Language (Contd.)

ABAP Objects is not a new language, but a systematic extension of ABAP.

Type checks in ABAP Object context is stricter.

Cleaner Syntax: Obsolete statements lead to syntax errors.

ABAP object statements can be used in procedural ABAP programs.

Object (Classes) can also contain procedural ABAP statements.

Although a pure OO world is technically possible, most real-worldimplementations use a mixture of procedural ABAP and ABAP Objects.



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Why do we need to learn ABAP Objects ?

To understand the recent concepts of ABAP e.g. BAPI, BAdi, Workflow.

ABAP Objects is the only way you can use new ABAP technology. For example

all new GUI concepts, such as the SAP Control Framework (CFW) and Business

Server Pages (BSP), are encapsulated in ABAP Objects classes.

For interfacing ABAP with Microsoft technologies or Java as all these are built on

the OOP concept. To take advantage of cleaner syntax and semantic rules.

To exploit the object resource that has been provided by SAP.



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Classes ( Global + Local )

A class is a template/blueprint based on which all objects of the class arecreated. Class does not occupies any memory space during program

execution only the instance of an class (objects) occupies memory space. In ABAP, classes can be of two types:

Global Class (Created using class builder (SE24) and stored in class repository

as Class pool) Local Class (Created in any ABAP program in global declarations section and

only accessible to the programs within the main program.)

Global vs. Local Classes Global Classes Local Classes

Accessed from ? Any Program Only with in the Program where itis defined

Where store ? In the class repository Locally in the program where it isdefined

Tools required to create ? Class builder (SE24) With ABAP editor (SE38)

Namespace ? Must begin with ‘Y’ or ‘Z’ Any



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Declaring a Class: Local

Classes are template for Objects.

This example declares and defines a

local class “test ”.

The class DEFINITION belongs in

the global declarations section at the

beginning of the program. Class definition cannot be nested.

Classes cannot be defined inside

subroutines or function modules.

A class definition declares :

Its components :

Attributes, Methods, Events.

The visibility of its components :

Public, Protected and Private.

A class declaration has two parts.

Definition

Implementation

CLASS test DEFINITION.

PUBLIC SECTION.{ Attributes, Methods, Events }

PROTECTED SECTION.

{ Attributes, Methods, Events }

PRIVATE SECTION.

{ Attributes, Methods, Events }

ENDCLASS.

CLASS test IMPLEMENTATION.

<class body>

{Method implementation is done here}

ENDCLASS.



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Components of Class ( Instance + Static )

Instance components: DATA

For instance attributes

METHODS

For instance methods

EVENTS For instance events

Static components:

CLASS-DATA

For static attributes

CLASS-METHODS For static methods

CLASS-EVENTS

For static events

CONSTANTS

For constants

Instance components exist separately in eachinstance (object) of the class.

Static components only exist one per class and

are valid for all instances of the class.

Static attributes of a class are retained

throughout the entire runtime. Static components are declared with the

CLASS- * keywords.

To access instance components, instance

component selector (->) is used.

To access static components, static componentselector (=>) is used.



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Instance vs. Static components: Elaborated

The class components that share a common memory area for all the classinstance are static components.

The class components that have separate memory area for separate instance are

instance components.

Object 1 of Class Object 2 of Class Object 1 of Class Object 2 of Class

Memory for

Object 1

Memory for

Object 2

Memory for Object 1

and

Object 2

Instance Static



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Visibility sections in a Class

All components of a class must belong to a visibility section. Components canbe public, protected or private.

Public components form the external interface of the class – they are visible toall users of the class as well as to methods within the class and to methods of subclasses.

Protected components form the interface of the class to its subclasses they are

visible to methods of the heirs of the class as well as to methods within the class. Private components can only be used in the methods of the class itself. Using

private visibility section is known as Encapsulation or Information hiding.

Notes:

There is no default visibility section in a class.

You should not make attributes public unless absolutely necessary.



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Attributes

Attributes contains data that can bestored in the objects of a class.

Attributes can be of 3 types:

elementary, structured or table-type.

In classes you can only use TYPE

addition to refer to data types and useLIKE reference only for local data

objects.

The READ ONLY addition can be

used for data declared in PUBLIC

SECTION, which means the data can

be read from outside, but can bechanged only by methods of the same

class.

CLASS c1 DEFINITION.PUBLIC SECTION.

METHODS: do_something…

PRIVATE SECTION.

TYPES: ……

CONSTANTS: ……DATA:

var1 TYPE local_type,

var2 TYPE global_type,

var3 LIKE var1,

var4 TYPE built_in_type VALUE val,var5 TYPE local_type READ-ONLY,

var6 TYPE REF TO class_name.

ENDCLASS.



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Methods


METHODS: do_something

IMPORTING ...i1 TYPE…

EXPORTING…e1 TYPE…

RETURNING VALUE (P)

.. R1 TYPE…CHANGING …c1 TYPE…

EXCEPTIONS …en.

PRIVATE SECTION.

DATA: …

ENDCLASS.

CLASS c1 IMPLEMENTATION.

METHOD do_something.

…

ENDMETHOD.

ENDCLASS.

Methods are the functionality of aclass , ABAP code is written within a

method to incorporate the

functionality.

Methods are processing blocks with a

parameter interface very similar to

function modules.

Methods are of two types:

Standard Methods.

e.g. METHODS meth.

Event handler methods:

METHODS meth FOR EVENT evt OF

class.This type of methods are written to

trap events.

Methods are called with a CALL

METHOD statement.

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Methods (Contd.)

Methods have a signature. With function modules, you should type eachparameter but are not forced to do so; with methods, you must type each

parameter.

Standard methods are declared, with their parameter interface, in the class

definition part and implemented in the class implementation part.

All input parameters (IMPORTING & CHANGING) can have OPTIONAL or DEFAULT addition and then these parameters need not be transferred when the

method is called.

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Constructors

METHODS constructor IMPORTING im_par TYPE string.

CREATE OBJECT obj

EXPORTING im_par = val_ex.

CLASS-METHOD class_constructor

Constructor is a special method that iscalled by the runtime system as soon as

the object is created with the CREATE

OBJECT statement.

Useful for:

Initializing data structures or setting

default values to attributes dynamically.

Sending message about object creation.

Each class has one constructor. It is a

predefined with the name

CONSTRUCTOR (or

CLASS_CONSTRUCTOR for static

constructor).

Constructors should be defined in the

public area.

Instanceconstructor

Static

Constructor

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Constructors (Contd.)

Instance constructor can only have IMPORTING PARAMETERS &EXCEPTIONS. It has no EXPORTING parameters because its sole purpose is toinitializing the object.

The Static constructor method has no interface parameters.

The Static constructor is called automatically when the class is first accessed:

Creating an instance of the class (CREATE OBJECT)

Accessing a static attribute or Method of the class.

Registering an event handler method for an event in this class.

A static constructor can’t be called explicitly

When exception is raised in an instance constructor, instances are not created,

thus no memory space is occupied.

Notes:

There is no Destructor in ABAP Objects. I.e. there is no instance method

automatically called immediately before the object is deleted.

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Some more features of Class

CLASS class_name DEFINITION DEFERRED. This is used in forward referencing.

CLASS class_name DEFINITION LOAD.

If the first access to a global class in a program is to its static components then explicit

loading of the class definition is necessary. In release 6.40 this statement is not

required. CLASS class_name DEFINITION CREATE PUBLIC| PROTECTED | PRIVATE.

‘CREATE PUBLIC’ addition is provided automatically by compiler if no create

addition is used.

The additions CREATE PROTECTED and CREATE PRIVATE allow you to

control the instantiation of your class.

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DATA: int TYPE I VALUE ’10’.

METHODS display_int.

ENDCLASS.

CLASS c1 IMPLEMENTATION.METHOD display_int.

WRITE / int.

ENDMETHOD.

ENDCLASS.

DATA : oref TYPE REF TO c1.START-OF-SELECTION.

CREATE OBJECT oref.

WRITE / oref-> int.

CALL METHOD oref-> display_int.

Objects and Object references

Objects are real runtime replica of classes.

Objects can only be created and

addressed using reference variables.

To use objects:

Declare reference variables with typeof the class.

Create objects, assigning their

references. (This is called

Instantiation)

Use the object components.

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Self- Reference


DATA: int TYPE I VALUE ’10’.

METHODS display_int.

ENDCLASS.


METHOD display_int.

DATA : int TYPE I VALUE ’20’.

WRITE:/ int,

ME->int.

ENDMETHOD.ENDCLASS.

DATA : oref TYPE REF TO c1.

CREATE OBJECT oref.

CALL METHOD oref-> display_int.

If an objects internally needs toprovide its own reference, it can use

the local reference variable “ME”.

“ME” is predefined and always

contains a reference to the address

of its own object.

Notes:

“ME” is equivalent to “THIS” pointer

in C++.

Local variable of the Method

Variable of the Class

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Multiple instantiation


METHODS meth.

ENDCLASS.


…ENDCLASS.

DATA: oref1 TYPE REF TO c1,

oref2 TYPE REF TO c1.

START-OF-SELECTION.CREATE OBJECT: oref1, oref2.

…

Programs can instantiate multipleobjects of the same class.

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Deleting Objects

…

DATA: oref1 TYPE REF TO c1,


...

CREATE OBJECT: oref1, oref2.

…

oref1 = oref2.

CLEAR oref1.

CLEAR oref2.

oref2

oref1

9999oref2

oref1

8888Object of C2

Object of C1

8888oref2

oref1

8888

oref2

oref1

8888

9999

8888

Object of C2

Object of C19999

Object of C2

Object of C19999

8888

8888

Object of C2

Object of C19999

8888

oref1

oref2

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Calling Methods

CALL METHOD oref->methEXPORTING im_par1 = val_ex1…. im_par(n)= val_ex(n)…

IMPORTING ex_par = val_im…

CHANGING ch_par = val_chg…

RECEIVING ret_par = val_res...

EXCEPTIONS exception = val_rc…

Shorter Syntax available from SAP Web AS 6.10

oref->meth(

EXPORTING im_par1 = val_ex1…. im_par(n)= val_ex(n)…

IMPORTING ex_par = val_im…

CHANGING ch_par = val_chg…RECEIVING ret_par = val_res...

EXCEPTIONS exception = val_rc…)

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Functional Methods

METHODS methIMPORTING…

RETURNING VALUE (r)…

CALL METHOD oref->meth

EXPORTING i1 = a1….in = anRECEIVING r = a.

Example:

var = oref->meth().

or var = oref->meth(a).

or

var = oref->meth( i1 = a1….in = an).

Instead of CALL METHOD,functional methods can be

performed in expressions.

A Functional method can have

zero to many IMPORTING

parameters, EXCEPTIONS

and exactly one RETURNING

parameter, that must be

passed by value.

A Functional method can be

instance or static method.

Operands can be replaced byfunctional methods

Conventional

Method call

Method callspecific to

Functionalmethod

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Pointer tables

DATA: oref1 TYPE REF TO c1,oref2 TYPE REF TO c1,


DATA: oref TYPE REF TO c1,

oref_tab TYPE TABLE OF REF TO c1.

START-OF-SELECTION.

…

DO 3 TIMES.

CREATE OBJECT oref.

APPEND oref TO oref_tab.

ENDDO.

…

LOOP AT oref_tab INTO oref.

CALL METHOD oref->meth.

ENDLOOP.

Pointer tables are used to storemultiple instances/objects of

same class. This method

reduces coding and more

elegant against creating

separate, separate object

reference variables for storingevery objects of the same class.

Reference variables are

handled like any other data

object with an elementary data

type.

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Dynamic Method calls


METHODS: meth1, meth2.

…

DATA fld TYPE …

DATA oref TYPE REF TO c1.…

CREATE OBJECT oref.

…

Do something to assign meth1

or meth2 to fld at runtime.

fld = ‘METH1’ or ‘METH2’.

CALL METHOD oref->(fld).

Instance, self-reference, and static methodcan all be called dynamically; the class

name for static methods can also be

determined dynamically:

Variants:

- oref->(method)- me->(method)

- class=>(method)

- (class)=>method

- (class)=>(method)

A method’s parameters can be passed

dynamically using PARAMETER-TABLE

and EXCEPTION-TABLE additions to the

CALL METHOD statement.

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Demonstration

Creating a local class with different components in different visibility sections andshowing how to instantiate the class as well as how to access the instance and

static components.

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Practice

Creating a local class with different components in different visibility sections andshowing how to instantiate the class as well as how to access the instance and

static components.

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Summary

Features of Object oriented programming are: Abstraction

Ecapsulation

Inheritance

Polymorphism

Code Reuse

Classes and Objects are the basic building blocks of Object Oriented

Programming When a real world entity is modeled into OOP world then it is known as Class,

characteristics as attributes and functionality as methods. Objects is an instance of a Class. Classes can be of two types:

Global Class (Created using class builder (SE24) and stored in class repository as

Class pool) Local Class (Created in any ABAP program)

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Questions

What kind of Programming language is ABAP ?

What version of SAP first released ABAP Objects ?

Can class definition be nested ?

Can you define a local class within a subroutine or function module ?

What is the default visibility section in a class ?

Can you call a constructor with the CALL METHOD statement ?

What Interface parameters does a Static Constructor have ?

When is CLASS class_name DEFINITION DEFERRED statement required ?

What parameters does a Functional method have ?

Which transaction we use to maintain global class? What are the various visibility sections present in a ABAP class?

What is the basic difference between static component and instance

component ?

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Questions

Can we access the static component of a class by the object name instead of theclass name?

What are the main advantages of Object Oriented Programming over Procedural

Programming ?

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Hands-on Exercises

Exercise 1:

Exercise 2:

chapter 01_fundamentals of abap object

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