topic Re: Singleton design pattern in OO ABAP in Application Development and Automation Discussions

Singleton design pattern in OO ABAP

former_member632800 — Mon, 23 Nov 2020 12:24:28 GMT

Hi,

Please explain the Singleton design pattern with an example.

If you know any requirement you worked on please explain.

Regards,

Manjunath M

Re: Singleton design pattern in OO ABAP

MateuszAdamus — Mon, 23 Nov 2020 12:26:52 GMT

Hello manjunathm

http://zevolving.com/2008/09/abap-object-design-patterns-singleton/

Kind regards,
Mateusz

Re: Singleton design pattern in OO ABAP

nmirandaghn — Mon, 23 Nov 2020 15:17:17 GMT

Singleton pattern restricts multiple instantiation of a class by just letting create one instance.

The following is a short example of the singleton pattern.

report zsingleton.

class cl_singleton definition.
  public section.
    class-data p_my_class type ref to cl_singleton.
    class-methods get_instance returning value(r_my_class) type ref to cl_singleton.
endclass.

class cl_singleton implementation.
  method get_instance.
    if p_my_class is initial.
      write / 'Created new instance'.
      p_my_class = new #( ).
    else.
      write / 'Do not create new instance. Just return the same created before'.
    endif.
    r_my_class = p_my_class.
  endmethod.
endclass.

data lcl_my_class type ref to cl_singleton.

start-of-selection.

lcl_my_class = cl_singleton=>get_instance(  ). " -> Output: Created new instance
lcl_my_class = cl_singleton=>get_instance(  ). " -> Output: Do not create new instance. Just return the same created before
lcl_my_class = cl_singleton=>get_instance(  ). " -> Output: Do not create new instance. Just return the same created before

break-point.

For more information visit this link: https://en.wikipedia.org/wiki/Singleton_pattern.

Re: Singleton design pattern in OO ABAP

former_member702682 — Wed, 25 Nov 2020 03:32:07 GMT

Hi manjunathm

* Singleton means Private instantiation and globally access.

* Singleton class object create with in the class only we cant create a object outside the class but we can access the components of that singleton class.

* Creating a class in such way so that we can create exactly one object is called as singleton.

REPORT ZAK_SINGLETON.

class ZCL_SINGLETON_LOGIN definition
final
create private .

public section.

class-methods LOGIN.

private section.

class-data LV_INST type ref to ZCL_SINGLETON_LOGIN .

class-methods INSTANCE
returning
value(RO_INST) type ref to ZCL_SINGLETON_LOGIN .

ENDCLASS.

CLASS ZCL_SINGLETON_LOGIN IMPLEMENTATION.

method INSTANCE.

IF LV_INST IS NOT BOUND.
CREATE OBJECT RO_INST.
LV_INST = RO_INST.
ELSE.
RO_INST = LV_INST.
ENDIF.
endmethod.

method LOGIN.
write : 'Demo For Singleton'.
endmethod.

ENDCLASS.

START-OF-SELECTION.

ZCL_SINGLETON_LOGIN=>LOGIN( ).

Thankyou.

Re: Singleton design pattern in OO ABAP

FredericGirod — Wed, 25 Nov 2020 14:54:31 GMT

WIth SingleTon, I think the most important is to show that, two separated report access the same instance :

https://answers.sap.com/questions/12988109/how-do-we-use-singleton-in-oo-abap-can-someone-ple.html