topic Re: Is A SubClass Self-Aware ? in Application Development and Automation Discussions

Is A SubClass Self-Aware ?

mike_mcinerney — Thu, 24 Sep 2009 20:45:13 GMT

Let's say we have a superclass, zcl_animal. It has subclasses zcl_cat and zcl_dog with methods meow() and bark() respectively.

Let's say we set up an internal table called it_animals of type ref to zcl_animal.

I create a number of cats and dogs and append their refs into it_animals.

Furthermore,

lo_animal is type ref to zcl_animal

lo_cat is type ref to zcl_cat

lo_dog is type ref to zcl_dog

Now I loop through animal into the generic lo_animal object

Is there anyway for lo_animal to tell what subclass (cat or dog) it is so I can cast it appropriately.

(without trial and error casting )?

Thanks...

...Mike

Re: Is A SubClass Self-Aware ?

naimesh_patel — Thu, 24 Sep 2009 20:50:21 GMT

You can use the RTTS to get the class name and get to know which subclass it is.

Method get_class_name of class CL_ABAP_CLASSDESCR.

Or, You can create an additional column in internal table which carries the name of the object as well.

Regards,

Naimesh Patel

Re: Is A SubClass Self-Aware ?

naimesh_patel — Thu, 24 Sep 2009 20:56:31 GMT

One more thought. (I haven't tested it)

You can create a protected method say ACTION( ) in your class ZCL_ANIMAL. Redefine this method in all subclasses. In the redefinition of method ACTION( ) in subclass ZCL_CAT, call method ME->MEOW( ).

This way, your application would not know, which sub-object it is dealing with. It would call the ACTION method and action would decide what to call from Sub-class.

Regards,

Naimesh Patel

Re: Is A SubClass Self-Aware ?

mike_mcinerney — Thu, 24 Sep 2009 21:03:55 GMT

Thanks - your first response was what I was looking for.

Redefinition (which I have a handle on) does not work in my

general case of the underlying problem, as some of the animals,

using this example, are giraffes and do not make a sound

(ie many of our methods won't be applicable across all subclasses)

Thanks for your help

...Mike

Re: Is A SubClass Self-Aware ?

nomssi — Sat, 26 Sep 2009 22:25:17 GMT

Hi,

your reference to Giraffe made me think you might need delegation instead of inheritance.

(i.e. STRATEGY PATTERN e.g. at http://sourcemaking.com/design_patterns/strategy).

regards,

Jacques Nomssi Nzali