doubt in casting

lokesh_kamana — Wed, 24 Oct 2007 04:21:33 GMT

hi sdns,

i am new to OOABAP.I am being trained on this concepts.I am facing a lot of difficulty in understanding Narrowing Cast & Widening Cast.I have some doubts in that.

i have a doubt in widening cast.I Know that we are increasing the scope with the same object in widening cast.

if we have two classes airplane,cargo_airplane

DATA: airplane TYPE REF TO lcl_airplane,

cargo_airplane TYPE REF TO lcl_cargo_airplane,

cargo_airplane2 TYPE REF TO lcl_cargo_airplane.

CREATE OBJECT cargo_airplane.

airplane = cargo_airplane.

cargo_airplane2 ?= airplane.

if we have a method in airplane.we have a redefined it in cargo_airplane.

After this widening cast.

if we acccess this method from cargo_airplane2.

which method will it access redefined method or the method in super class.

please do explain me this example clearly.

with regards,

lokesh

Re: doubt in casting

Former Member — Mon, 29 Oct 2007 16:52:56 GMT

Hi Lokesh,

The redefined method will be accessed.

Regards

Bhooma

Re: doubt in casting

sreekanthgo — Mon, 29 Oct 2007 17:55:13 GMT

Hi Lokesh,

Let me explain you about this using another example than your example which would gives you a better understanding on the casting.

The use of casting is to assign the same memory location to both the classes.

Let us assume that there are two classes,

1) Animal ( Class )

2) Dog ( Class )

Dog inherits all properties from the Animal, So Dog is the child class and Animal is the Super class.

If i create the instance of the Animal class and Assigns the same to the Dog, it is called as the Widening casting ( or Down Casting ).

If I do reverse to it... If I create the Dog object and assigns the same to the Animal, this is called as the Narrowing casting ( or Up Casting )

Below example would give you a better idea on casting and it would also answers your question properly.



*----------------------------------------------------------------------*
*       CLASS C1 DEFINITION
*----------------------------------------------------------------------*
*
*----------------------------------------------------------------------*
CLASS C1 DEFINITION.
  PUBLIC SECTION.
    data: var1 type ref to object.
    METHODS: METH1.
ENDCLASS.                    "C1 DEFINITION
*----------------------------------------------------------------------*
*       CLASS C1 IMPLEMENTATION
*----------------------------------------------------------------------*
*
*----------------------------------------------------------------------*
CLASS C1 IMPLEMENTATION.
  METHOD METH1.
    WRITE: / 'This is a method one in class C1'.
  ENDMETHOD.                                                "METH1
ENDCLASS.                    "C1 IMPLEMENTATION
*----------------------------------------------------------------------*
*       CLASS C2 DEFINITION
*----------------------------------------------------------------------*
*
*----------------------------------------------------------------------*
CLASS C2 DEFINITION inheriting from c1.
  PUBLIC SECTION.
    METHODS: METH2, meth1 redefinition.
ENDCLASS.                    "C2 DEFINITION

*----------------------------------------------------------------------*
*       CLASS C2 IMPLEMENTATION
*----------------------------------------------------------------------*
*
*----------------------------------------------------------------------*
CLASS C2 IMPLEMENTATION.
  METHOD METH2.
    WRITE: / 'This is a method two'.
  ENDMETHOD.
   METHOD METH1.
    WRITE: / 'This is a method one in class C2'.
    call method super->meth1.
   ENDMETHOD.
ENDCLASS.                    "C2 IMPLEMENTATION

START-OF-SELECTION.

  DATA REF1 TYPE REF TO C1.
  DATA REF2 TYPE REF TO C2.

  CREATE OBJECT REF2.
  ref1 = ref2.
  ref2 ?= ref1.

  call method ref1->meth1.

Thanks,

Sreekanth

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