Narrow Casting Vs Widening Casting

[Former Member]

Hello,

Can anybody please explain me the difference with an example between <b><i>Narrow Casting</i></b> and <i><b>Widening</b></i> <i><b>Casting</b></i> in ABAP Objects.

Regards

Kalyan

[Lakshmant1]

Hi Aswani,

Have a look at this url

http://help.sap.com/saphelp_47x200/helpdata/en/c3/021959f06111d4b2eb0050dadfb92b/frameset.htm

Thanks

Lakshman

[ssimsekler]

Hi Kalyan

In fact, the names imply everything. Let me illustrate a bit. This illustration will deal with one aspect which I think will be enough at least to understand the concept simply. Think of two instances (objects) of two classes one of which is inherited from the other, that is; one is a general class and the other is a specialized class of it.

<u>e.g.</u>

Class 1 --> land_vehicle

Class 2 --> truck

The class <b>land_vehicle</b> has following attributes:

  max_speed
  number_of_wheels
  number_plate
  ...

The class <b>truck</b> has following attributes:

  max_speed [inherited]
  number_of_wheels [inherited]
  number_plate [inherited]
  <i>load_capacity</i> [special to truck class]

Now, assume you have instantiated these classes as

<b>"land_vehicle_obj"</b> and <b>"truck_obj"</b> respectively from these classes.

Between these two objects, you can assign one to the other and at this point casting occurs.

i. If you assign <i>truck_obj</i> to <i>land_vehicle_obj</i> you lose the special attribute <i>load_capacity</i> since you go from the specialized on to the general one. Thus, this is a <b>narrowing cast</b>.

i. If you assign <i>land_vehicle_obj</i> and <i>truck_obj</i> you do not lose any attribute, nevertheless you add a new one. Thus this is a <b>widening cast</b>.

Regards

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