Restricting Multiple Instances

[Former Member]

Hi,

How to create a Private Class & Restrict Multiple Instantiations.

Regards,

Ravi S

[uwe_schieferstein]

Hello Ravi

I assume you are talking about the SINGLETON pattern.

Define the instantiation of your class as private.

Define a static private attribute MO_INSTANCE of TYPE REF TO <name of your class>.

To instantiate you need a static method (e.g. CREATE) which return an instance of your class (e.g. RETURNING parameter RO_INSTANCE).

METHOD create.

  IF ( mo_instance IS BOUND ).
    ro_instance = mo_instance.
  ELSE.
    CREATE OBJECT mo_instance. 
    ro_instance = mo_instance.    
  ENDIF.
    

ENDMETHOD.

Regards

Uwe

[GrahamRobbo]

Hi Ravi,

in addition to Uwe's advice you should define the class with "PRIVATE" instantiation. This has the effect of making it impossible to instantiate the class from outside itself - so only Uwe's CREATE method can be used to instantiate it.

There is a good SAP Press publication that covers this. It is called "Design Patterns in Object-Oriented ABAP" by Igor Barbaric.

Cheers

Graham Robbo

[Former Member]

Hi Ravi,

Through SE24 T-code we can handle the access specifiers(Public,Private,Protected) of a class.

While creating a class with SE24,the second screen's Instantiation field contains - 'Public,Private'..here we can declare Private to make the class private.This is the best way to handle the visibility of a class.

And among the checkboxes 'Final & Only Modeled' ,only Final must be checked for this class to have no more instances.

Do reward me if you find helpful.

[matt]

>

> And  among the checkboxes 'Final & Only Modeled' ,only Final must be checked for this class to have no more instances.
> 
> Do reward me if you find helpful.

This is not correct. Final prevents subclassing. It has no effect whatsoever on instantiation.