Author: Rudramani Pandey

Preface – This post is part of the Object Oriented ABAP series.

Introduction

Events in ABAP Class are the functions in a class which triggers the event handlers of other class based on the outcomes. With the use of events, any number of event handler methods can be called. The link between the triggering event and event handler is decided at run-time.

Definition

An event is the mechanism by which a method of one class can invoke the method of other class without instantiating that class.

Steps to add Events in ABAP Class

• Define an event
• Define a method
• Link event and method
• Create a triggering method to raise the event
• Define SET HANDLER statement at an instance in the program

Points to consider

• Event handler method is defined by FOR EVENT <event-name> OF <class-name>.
• It has only output parameters.
• To pass output parameters to the event handler method, RAISE EVENT statement is used.
• SET HANDLER method is used to link the event to its handler methods in a program.

Types of Events

Events are of two types:

• Instance events: Instance events can only get triggered in instance methods. It is declared using EVENTS statement.

EVENTS <event-name>….

• Static events: Static events are triggered by both instance and static methods. And also static methods can only trigger static events. It is declared using CLASS-EVENTS.

CLASS-EVENTS <event-name>….

Syntax

FOR EVENT <event-name> OF <class-name>.

Example

Lets’ pin down an example:

**** main class definition****

CLASS zcl_demo DEFINITION.

PUBLIC SECTION.

DATA : num1 TYPE I.

METHODS: compare IMPORTING num2 TYPE I.

EVENTS: event_compare.

ENDCLASS.

****event handler definition****

CLASS zcl_eventhandler DEFINITION.

PUBLIC SECTION.

METHODS: handling_compare FOR EVENT event_compare OF zcl_demo.

ENDCLASS.

****class implementation ****

CLASS zcl_demo IMPLEMENTATION.

METHOD compare.

num1 = num2.

If num1 > 10.

RAISE EVENT event_compare.                                                              “Raise an event

ENDIF.

ENDMETHOD.

ENDCLASS.

 

****event handler implementation ****

CLASS zcl_eventhandler IMPLEMENTATION.

METHOD handling_compare.

WRITE: “Event triggered… Num1 is greater than 10..”

 

ENDMETHOD.

ENDCLASS.

START-OF-SELECTION.

****creating class object****

DATA : object_demo TYPE REF TO zcl_demo,

****creating event handleobject****

object_eventhandler TYPE REF To zcl_eventhandler.

CREATE OBJECT object_demo.

CREATE OBJECT object_eventhandler.

SET HANDLER object_eventhandler-> handling_compare FOR zcl_demo.        “Setting up handler

object_demo-> compare(2).

Preface – This post is part of the Object Oriented ABAP series.

Introduction

As we know that the principles of Object-Oriented Programming are Encapsulation, Abstraction, Inheritance and Polymorphism. Polymorphism is implemented through Interfaces. It defines the ability of a message to be displayed in many forms. It allows an interface to have multiple implementations.  In this article we will discuss Interface in ABAP OOPs in detail.

Consider a real-life example; a person at the same time has many roles. A woman at the same time can have many features, she can be a mother, wife, daughter or an employee but actions are as per the situation and conditions. Similarly, an interface is an independent entity which can have many implementations to extend the scope of the classes.

Properties of Interface

• Interfaces only have method definitions. Method implementation is done in implemented classes.
• Interfaces can be used by any no of classes to extend the scope of the class.
• Each class can have its own implementation of interface methods depending upon the class functionalities.
• The declaration of interface does not include the visibility section. But in the declaration part of a class, they must be listed under Public Section.

You can create an interface in SE24. Provide the interface name, methods and its parameters and implement the interface in classes.

Definition of Interface in ABAP

Interface is an independent structure which is used in classes to enhance its functionality.

Example

Let’s pin down an example.

****interface definition****

INTERFACE zif_demo.

METHOD display.

ENDINTERFACE.

****class definition ****

CLASS zcl_demo DEFINITION.

PUBLIC SECTION.

INTERFACES zif_demo.

END CLASS.

CLASS zcl_demo1 DEFINITION.

PUBLIC SECTION.

INTERFACES zif_demo.

END CLASS.

 

****class implementation****

CLASS zcl_demo IMPLEMENTATION.

METHOD zif_demo~display.                                                              “Interface Method implementation

WRITE : “This is the interface method in class 1..”

END METHOD.

END CLASS.

CLASS zcl_demo1 IMPLEMENTATION.

METHOD zif_demo~display.                                                              “Interface Method implementation

WRITE : “This is the interface method in class 2..”

END METHOD.

END CLASS.

 

****creating class object****

START-OF-SELECTION

DATA : object_demo TYPE REF TO zcl_demo.

CREATE OBJECT object_demo.

CALL METHOD : object_demo-> zif_demo~display.

 

DATA : object_demo1 TYPE REF TO zcl_demo1.

CREATE OBJECT object_demo1.

CALL METHOD : object_demo1-> zif_demo1~display.

In the above example, there is one interface zif_demo defined which has only the definition part. And we have two classes zcl_demo and zcl_demo1 implementing the interface. This is how we can achieve Polymorphism through interfaces.

Preface – This post is part of the Object Oriented ABAP series.

Introduction

An alias in general term is used to indicate the alternate name for a given person, or thing. Similarly, in OOPs ABAP, an alias is an alternate name given to the interface methods implemented in the class. Whenever we implement the interface in a class, the interface method is copied with naming convention <Interface-Name>~<Method-Name>. Instead of using the default interface method name in the class, we can provide an alternate name to it (called alias) and can use alias name in the program. In this article we will learn more about Alias in SAP Classes.

Definition

An alias is an alternate name for interface methods that are implemented in the class.

How to give alias name to interface methods in the SAP Classes?

In transaction SE24, provide the class name and open it in editable mode. There will be one Alias tab. Provide the alias name corresponding to the interface methods.

Calling interface methods in the class will be easy by the use of an alias.

CALL METHOD <object-name> -> <alias-interface-method>

Syntax

The below syntax is used to give alias in the program:

ALIASES  <alias-name> FOR <interface-method>.

Example

Let us suppose an interface is implemented in the class and we have provided alias name to the interface method.

For example,

ZIF_MATERIAL~GET_MATERIAL_DETAILS (Interface Method)    –       DETAILS (Alias Name)

DATA : object_name TYPE REF TO zcl_demo.

DATA: wa_mara TYPE MARA.                                                                      “MARA Declaration

PARAMETERS p_matnr TYPE MARA-MATNR.                                       “User Input

CREATE OBJECT object_name.                                                                   “Object creation

START-OF-SELECTION.

** CALL METHOD object_name -> ZIF_MATERIAL~GET_MATERIAL_DETAILS.**

 

CALL METHOD object_name -> details.                                                   “Method call with alias name

EXPORTING

IM_MATNR = p_matnr

IMPORTING

EX_MATNR = wa_mara.

The above code retrieves the material details based on the input material number (MATNR) from interface ZIF_MATERIAL. Here we have used the alias name DETAILS as method name for the simplicity of understanding the code. Instead of DETAILS, we can also use ZIF_MATERIAL~GET_MATERIAL_DETAILS, but using this more than once in tricky code will make the code much more complex.

Preface – This post is part of the Object Oriented ABAP series.

Introduction

A method defines the behaviour of an object. It can access all the attributes and hence can change the status of the object. In this article we will discuss Class Method in SAP OOABAP.

There are a few points to consider while declaring the method:

• The method definition is defined in the class definition and implemented in class implementation.
• It can be declared using Method and End method statement.
• Methods have parameter interface to pass the values when they are called and return the value to the caller.

Syntax

The method must be declared between the statements METHOD and END METHOD.

METHOD <method-name>.

.

.

END METHOD.

Types

There are three types of methods:

• Instance method

  These methods are declared using METHOD statements. They can access all the attributes of the class and can trigger all the events.

• Static methods

  These types of method are declared using CLASS-METHOD statements. They can access the static attributes and can trigger static events only.

• Special methods

  There are two special methods : constructor and class_constructor, which are called automatically whenever the class is accessed for the first time.

ME Operator in Class Method

In the implementation part of the instance method in a class, an implicitly created local reference variable ME is available. It points to the currently executed instance. The me variable is reserved and cannot be used for naming attributes and parameter.

Example

****class definition****

CLASS zdemo DEFINITION.

       PUBLIC SECTION.

             DATA var(50) TYPE C VALUE “Displaying me variable”.

                METHOD instance_method.                                                        “Instance Method definition

                CLASS-METHODS static_method.                                              “Static Method definition

END CLASS.

****class implementation****

CLASS zdemo IMPLEMENTATION.

       METHOD instance_method.                                                                “Instance Method implementation

                WRITE : ME->var.                                                                             “ Displaying ME Variable

                WRITE : “This is instance method”

       END METHOD.

       METHOD static_method.                                                                      “Static Method implementation

                WRITE : “This is static method”

       END METHOD.

END CLASS.

****creating class object****

START-OF-SELECTION

DATA : object_demo TYPE REF TO zdemo.

CREATE OBJECT object_demo.

CALL METHOD : object_demo-> instance_method ,

                                object_demo->static_method.

Preface – This post is part of the Object Oriented ABAP series.

Introduction

Objects in ABAP are special variables that have distinct characteristics and behaviors in general terms known as attributes and methods. The attributes define the state of an object and a method defines the behavior or actions performed by the object.

An object has three main characteristics-

• State – State defines the set of attributes and its values.
• Identity – Each object has a unique identity.
• Behaviour – Behaviour defines the actions performed.

The two objects may have the same state or behaviour but their identity is always unique. The identity of object sustains till its lifetime.

For example, a student has attributes like student name (first name, last name), student id, date of birth, address and behaviour would be the change in its attributes. The two students may have the same attributes and behaviour but they are not identical. Their identity is unique and will never change throughout their lifetime.

Objects interact with each other by sending messages.

Definition

An object is the instance of the class. It is a special variable that has distinct characteristics and behaviours.

ABAP Objects creation

Object creation includes two steps. They are as follows:

• Creating reference variable to class.

DATA : <object_name> TYPE REF TO <class_name>.

• Creating an object from the reference variable.

CREATE OBJECT : <object_name>.

Example

Let’s jot down an example.

****class definition****

CLASS zdemo DEFINITION.

                PUBLIC SECTION.

                                 METHOD : zdemo_method.

END CLASS.

****class implementation****

CLASS zdemo IMPLEMENTATION.

                METHOD zdemo_method.

                                WRITE : “ABAP Object”

                END METHOD.

END CLASS.

****creating class object****

START-OF-SELECTION.

DATA : object_demo TYPE REF TO zdemo.                                             “Creating reference variable”

CREATE OBJECT object_demo.                                                                   “Creating object”

CALL METHOD : object_demo->zdemo.

In the example, zdemo_method is the method defined in the public section of definition part of the class zdemo. The implementation part of the method is provided in the class implementation. Firstly, we have created the reference variable object_demo to the class and then created an object object_demo from the reference variable. The object_demo->zdemo calls of the method zdemo_method and executes the code inside the method.