Constructor of class A instantiating class B and vice versa

Question

Hi folks,
I have two classes, namely ZCL_EMPLOYEE and ZCL_USER.
ZCL_EMPLOYEE has an attribute USER type ref to ZCL_USER, populated by a "create object" statement in the constructor method.
ZCL_USER has an attribute EMPLOYEE type ref to ZCL_EMPLOYEE, also populated by a "create object" statement in the constructor method.
Thus when I instantiate one of the classes, this inevitably results in an endless loop.
Is there any way to avoid this? I guess it must be possible to catch already instanciated objects and re-use them rather than instantiating all the time, but how?
Thanks a lot for your help,
Patrick

Answer 1

Hello Patrick
Since you need to create a couple of instance at the same time this is a task I would solve with the FACTORY pattern, e.g.:
Both class contain static factory methods and the instantiation is set private as suggested by Matthew, e.g.:
DATA:
  lo_user     TYPE REF TO zcl_user,
  lo_empl    TYPE REF TO zcl_employee.
  lo_user = zcl_user=>create( id_uname = <username> ).
  lo_empl = zcl_employee=>create( id_pernr = <personnel number> ).
CREATE method of ZCL_USER:
METHOD create. 
  CREATE OBJECT ro_instance    " of TYPE REF zcl_user
    EXPORTING
      id_uname = id_uname
*      io_employee =                     " optional parameter for employee instance      
ENDMETHOD.
CREATE method of ZCL_EMPLOYEE:
METHOD create.
  CREATE OBJECT ro_instance    " of TYPE REF zcl_employee
    EXPORTING
      id_pernr = id_pernr
*      io_user  =                            " optional parameter for user instance
ENDMETHOD.
CONSTRUCTOR method of ZCL_USER:
METHOD constructor.
  IF ( io_employee IS BOUND ).
    me->mo_employee = io_employee.
  ELSE.
    " get PERNR via infotype 0105
    CREATE OBJECT me->mo_employee
      EXPORTING
        id_pernr = <personnel number>
        io_user  = me.
  ENDIF.
ENDMETHOD.
CONSTRUCTOR method of ZCL_EMPLOYEE:
METHOD constructor.
  IF ( io_user IS BOUND ).
    me->mo_user = io_user.
  ELSE.
    " get uname via infotype 0105
    CREATE OBJECT me->mo_user
      EXPORTING
        id_uname = <username>
        io_employee  = me.
  ENDIF.
ENDMETHOD.
Final remark: If you are not yet aware of class CL_PT_EMPLOYEE you may want to have a look at my Wiki posting
[Unified Access to All HR Infotypes|https://wiki.sdn.sap.com/wiki/display/Snippets/UnifiedAccesstoAllHR+Infotypes]
Regards
  Uwe