OO ABAP - friendship via interfaces

*&---------------------------------------------------------------------*
*& Report  YSAP_INTERFACES_FRIENDS
*&
*&---------------------------------------------------------------------*
*&
*&
*&---------------------------------------------------------------------*

REPORT  ysap_interfaces_friends.

*----------------------------------------------------------------------*
*       INTERFACE interface1
*----------------------------------------------------------------------*
*
*----------------------------------------------------------------------*
INTERFACE interface1.
*  PUBLIC SECTION.
  METHODS: interface1_method.
ENDINTERFACE.                                               "interface1

*----------------------------------------------------------------------*
*       CLASS class1 DEFINITION
*----------------------------------------------------------------------*
*
*----------------------------------------------------------------------*
CLASS class1 DEFINITION.
  PUBLIC SECTION.
    INTERFACES: interface1.
ENDCLASS.                    "class1 DEFINITION

*----------------------------------------------------------------------*
*       CLASS class1 DEFINITION
*----------------------------------------------------------------------*
*
*----------------------------------------------------------------------*
CLASS class2 DEFINITION.
  PUBLIC SECTION.
    INTERFACES: interface1.
ENDCLASS.                    "class1 DEFINITION

*----------------------------------------------------------------------*
*       CLASS class3_friend DEFINITION
*----------------------------------------------------------------------*
*
*----------------------------------------------------------------------*
CLASS class3_friend DEFINITION FRIENDS class1.
  PUBLIC SECTION.
    DATA: string1 TYPE string VALUE 'string of class3_friend'.
ENDCLASS.                    "class3_friend DEFINITION

*----------------------------------------------------------------------*
*       CLASS class1 IMPLEMENTATION
*----------------------------------------------------------------------*
*
*----------------------------------------------------------------------*
CLASS class1 IMPLEMENTATION.
  METHOD interface1~interface1_method.
    DATA: class3_friend_object TYPE REF TO class3_friend.
    CREATE OBJECT class3_friend_object.
    SKIP.
    WRITE: / 'Accessing string1 from class1 via interface1'.
    WRITE: / class3_friend_object->string1 COLOR 7.
    SKIP.
    ULINE.
    SKIP.
  ENDMETHOD.                    "interface1~interface1_method
ENDCLASS.                    "class1 IMPLEMENTATION


*----------------------------------------------------------------------*
*       CLASS class2 IMPLEMENTATION
*----------------------------------------------------------------------*
*
*----------------------------------------------------------------------*
CLASS class2 IMPLEMENTATION.
  METHOD interface1~interface1_method.
    DATA: class3_friend_object1 TYPE REF TO class3_friend.
    CREATE OBJECT class3_friend_object1.
    WRITE: / 'Accessing string1 from class2 via interface1'.
    WRITE: / class3_friend_object1->string1 COLOR 7.
    SKIP.
    ULINE.
    SKIP.
  ENDMETHOD.                    "interface1~interface1_method
ENDCLASS.                    "class2 IMPLEMENTATION

START-OF-SELECTION.

  DATA: class1_object TYPE REF TO interface1.

  CREATE OBJECT class1_object TYPE class1.

  class1_object->interface1_method( ).

  DATA: class2_object TYPE REF TO interface1.

  CREATE OBJECT class2_object TYPE class2.

  class2_object->interface1_method( ).