类的继承

*----------------------------------------------------------------------*
*       CLASS superclass DEFINITION   建立一个基类
*----------------------------------------------------------------------*
*
*----------------------------------------------------------------------*
CLASS superclass DEFINITION.
  PUBLIC SECTION.
    METHODS write_first.
    METHODS write_second.
ENDCLASS.                    "superclass DEFINITION

*----------------------------------------------------------------------*
*       CLASS subclass DEFINITION  建立派生类，派生类有定义自己的方法
*----------------------------------------------------------------------*
*
*----------------------------------------------------------------------*
CLASS subclass DEFINITION INHERITING FROM superclass.
  PUBLIC SECTION.
    METHODS write_third.
ENDCLASS.                    "subclass DEFINITION

*----------------------------------------------------------------------*
*       CLASS superclass IMPLEMENTATION  定义基类实现方法
*----------------------------------------------------------------------*
*
*----------------------------------------------------------------------*
CLASS superclass IMPLEMENTATION.
  METHOD write_first.
    WRITE: / 'The First method'.
  ENDMETHOD.                    "write_first
  METHOD write_second.
    WRITE: / 'The Second method'.
  ENDMETHOD.                    "write_second
ENDCLASS.                    "superclass IMPLEMENTATION

*----------------------------------------------------------------------*
*       CLASS subclass IMPLEMENTATION  定义派生类实现方法
*----------------------------------------------------------------------*
*
*----------------------------------------------------------------------*
CLASS subclass IMPLEMENTATION.
  METHOD write_third.
    WRITE: / 'The Third method'.
  ENDMETHOD.                    "write_third
ENDCLASS.                    "subclass IMPLEMENTATION

DATA:inher_obj TYPE REF TO subclass.

START-OF-SELECTION.
  CREATE OBJECT inher_obj.
  CALL METHOD:inher_obj->write_first,"派生类不但可以应用其寄存的基类下的所有方法
              inher_obj->write_second,"而且它能在此基础调用本身所定义的新属性
              inher_obj->write_third.