OOPS ABAP: Constructors With Example

Constructors:

• Constructor is a special type of method which is executed automatically when a object is created.
• It cannot be called using CALL METHOD.
• Constructors are methods with a predefined name.
• Multiple CONSTRUCTOR and CLASS_CONSTRUCTOR are not allowed with in a class.

 

Types of constructors:

CONSTRUCTOR (Instance Constructor)	CLASS_CONSTRUCTOR (Static Constructor)
Method name: CONSTRUCTOR	Method name: CLASS_CONSTRUCTOR
It contains import parameters only	It does not contain any parameters
static and instance attributes can be accessed	Only static attributes can be accessed
It is called every time when a object is created	It is called first time when a object is created
Used to set a default value for particular instance

Example:

*&---------------------------------------------------------------------*
*& Report ZVB_CONSTRUCTOR
*&---------------------------------------------------------------------*

REPORT zvb_constructor.

CLASS c1 DEFINITION.
  PUBLIC SECTION.
    METHODS: constructor IMPORTING  num TYPE i
                         EXCEPTIONS e1.
    CLASS-METHODS: class_constructor.
ENDCLASS.
*&---------------------------------------------------------------------*
*& Class (Implementation) C1
*&---------------------------------------------------------------------*
*&
*&---------------------------------------------------------------------*
CLASS c1 IMPLEMENTATION.
  METHOD constructor.
    IF num LT 1.
      RAISE e1.
    ELSE.
      WRITE:/ num.
    ENDIF.
  ENDMETHOD.

  METHOD class_constructor.
    WRITE: 'Static constructor'.
  ENDMETHOD.
ENDCLASS.

START-OF-SELECTION.

  DATA: lo_obj TYPE REF TO c1.

  CREATE OBJECT lo_obj
    EXPORTING
      num    = 21
    EXCEPTIONS
      e1     = 1
      OTHERS = 2.
  IF sy-subrc <> 0.
    WRITE: 'Num can not be zero'.
  ENDIF.

Output: Static constructor

              21

Static Constructor (Class_Constructor):
Static or Class constructors are triggered in following cases:
•When the object is instantiated for the class.
•When static attributes (class=>a) or methods (class=>method) are accessed from the class.
•Registering a static event handler method using SET HANDLER class=>meth for obj.
•Registering an event handler method of static event of the class.

You can create instance and static constructors by clicking the 'Constructor' and 'Class constructor' buttons in SE24.