Singleton Design Pattern

REPORT ZADN_SAMPLE.

*----------------------------------------------------------------------*
*       CLASS cl_applicationstate DEFINITION
*----------------------------------------------------------------------*
CLASS cl_applicationstate DEFINITION CREATE PRIVATE.

  PUBLIC SECTION.

    DATA : hostname TYPE c LENGTH 128,
           ip_addrs TYPE c LENGTH 15.

    CLASS-METHODS : getstate EXPORTING p_instance TYPE REF TO cl_applicationstate.

  PRIVATE SECTION.

    METHODS : constructor.

    CLASS-DATA : _instance TYPE REF TO cl_applicationstate.

ENDCLASS.                    "cl_ApplicationState DEFINITION


*----------------------------------------------------------------------*
*       CLASS cl_applicationstate IMPLEMENTATION
*----------------------------------------------------------------------*
CLASS cl_applicationstate IMPLEMENTATION.

  METHOD constructor.

  ENDMETHOD.                    "constructor

  METHOD getstate.

    IF _instance IS NOT BOUND.

      CREATE OBJECT _instance.

      p_instance = _instance.

    ELSE.

      p_instance = _instance.

    ENDIF.

  ENDMETHOD.                    "getstate

ENDCLASS.                    "cl_ApplicationState IMPLEMENTATION

START-OF-SELECTION.

  DATA : o1_cl_applicationstate TYPE REF TO cl_applicationstate,
         o2_cl_applicationstate TYPE REF TO cl_applicationstate.

  cl_applicationstate=>getstate( IMPORTING p_instance = o1_cl_applicationstate ).

  IF o1_cl_applicationstate IS BOUND.

    o1_cl_applicationstate->hostname = 'LOCALHOST'.
    o1_cl_applicationstate->ip_addrs = '127.0.0.1'.

  ENDIF.

  cl_applicationstate=>getstate( IMPORTING p_instance = o2_cl_applicationstate ).

  WRITE / : o1_cl_applicationstate->hostname,
            o1_cl_applicationstate->ip_addrs.

  ULINE.

  WRITE / : o2_cl_applicationstate->hostname,
            o2_cl_applicationstate->ip_addrs.

  ULINE.

  IF o1_cl_applicationstate EQ o2_cl_applicationstate.

    WRITE / 'Objetos são iguais'.

  ENDIF.