ABAP Classes can be declared Globally or Locally. A global class can be used by any object within the ABAP repository. By contrast, a local class can only be used within the scope it is declared.

CLASS lcl_abap_class DEFINITION.
  PUBLIC SECTION.
  PROTECTED SECTION.
  PRIVATE SECTION.
ENDCLASS.

CLASS lcl_abap_class IMPLEMENTATION.
ENDCLASS.

Class implementation:

CLASS lcl_abap_class DEFINITION.
  PUBLIC SECTION.
    METHODS: constructor,
             method1.
  PROTECTED SECTION.
  PRIVATE SECTION.
    METHODS: method2,
             method3.
ENDCLASS.

CLASS lcl_abap_class IMPLEMENTATION.
    METHOD constructor.
        "Logic
    ENDMETHOD.

    METHOD method1.
        "Logic
    ENDMETHOD.

    METHOD method2.
        "Logic
        method3( ).
    ENDMETHOD.

    METHOD method3.
        "Logic
    ENDMETHOD.
ENDCLASS.

Method call example:

DATA lo_abap_class TYPE REF TO lcl_abap_class.
CREATE OBJECT lo_abap_class. "Constructor call
lo_abap_class->method1( ).

Class implementation:

CLASS lcl_abap_class DEFINITION.
  PRIVATE SECTION.
    METHODS method1 IMPORTING iv_string TYPE string
                     CHANGING cv_string TYPE string
                    EXPORTING ev_string TYPE string.
ENDCLASS.

CLASS lcl_abap_class IMPLEMENTATION.
    METHOD method1.
        cv_string = iv_string.
        ev_string = 'example'.
    ENDMETHOD.
ENDCLASS.

Method call example:

method1 (
  EXPORTING iv_string = lv_string
  IMPORTING ev_string = lv_string2
   CHANGING cv_string = lv_string3
).

Class implementation:

CLASS lcl_abap_class DEFINITION.
  PRIVATE SECTION.
    METHODS method1 RETURNING VALUE(rv_string) TYPE string.
ENDCLASS.

CLASS lcl_abap_class IMPLEMENTATION.
    METHOD method1.
        rv_string = 'returned value'.
    ENDMETHOD.
ENDCLASS.

Method call example:

lv_string = method1( ).

Note that parameters declared with RETURNING are passed by value only.

Information

Inheritance allows you to derive a new class from an existing class. You do this using the INHERITING FROM addition in the

CLASS subclass DEFINITION INHERITING FROM superclass.

statement. The new class subclass inherits all of the components of the existing class superclass. The new class is called the subclass of the class from which it is derived. The original class is called the superclass of the new class. A class can have more than one direct subclass, but it may only have one direct superclass.

Class implementation

CLASS lcl_vehicle DEFINITION.
ENDCLASS.

CLASS lcl_vehicle IMPLEMENTATION.
ENDCLASS.

CLASS lcl_car DEFINITION INHERITING FROM lcl_vehicle.
ENDCLASS.

CLASS lcl_car IMPLEMENTATION.
ENDCLASS.

Information

The ABSTRACT and FINAL additions to the METHODS and CLASS statements allow you to define abstract and final methods or classes.

An abstract method is defined in an abstract class and cannot be implemented in that class. Instead, it is implemented in a subclass of the class. Abstract classes cannot be instantiated.

A final method cannot be redefined in a subclass. Final classes cannot have subclasses. They conclude an inheritance tree.

---

Class implementation:

CLASS lcl_abstract DEFINITION ABSTRACT.
    PUBLIC SECTION.
        METHODS: abstract_method ABSTRACT,
                 final_method FINAL
                 normal_method.
                
ENDCLASS.

CLASS lcl_abstract IMPLEMENTATION.
    METHOD final_method.
        "This method can't be redefined in child class!
    ENDMETHOD.

    METHOD normal_method.
        "Some logic
    ENDMETHOD.

        "We can't implement abstract_method here!

ENDCLASS.

CLASS lcl_abap_class DEFINITION INHERITING FROM lcl_abstract.
    PUBLIC SECTION.
        METHODS: abstract_method REDEFINITION,
                 abap_class_method.
ENDCLASS.

CLASS lcl_abap_class IMPLEMENTATION.
    METHOD abstract_method.
        "Abstract method implementation
    ENDMETHOD.

    METHOD abap_class_method.
        "Logic
    ENDMETHOD.
ENDCLASS.

Method call example:

DATA lo_class TYPE REF TO lcl_abap_class.
CREATE OBJECT lo_class.

lo_class->abstract_method( ).
lo_class->normal_method( ).
lo_class->abap_class_method( ).
lo_class->final_method( ).