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Casting Object References

Shiaber Shaam
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Joined: Jun 16, 2006
Posts: 252
When we type cast object references..... we are casting the references or objects.... Plz clarify......


$Hi/\bEr
Keith Lynn
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Joined: Feb 07, 2005
Posts: 2367
You are casting the reference type. You can't cast an object.
Shiaber Shaam
Ranch Hand

Joined: Jun 16, 2006
Posts: 252
Ok.. then when do we need to cast references... can u explain some scenarios.... or rules.....
Keith Lynn
Ranch Hand

Joined: Feb 07, 2005
Posts: 2367
One situation where you need to cast references is if a method has a formal parameter which is a supertype of the actual parameter, then when the method is called, that reference will be widened. You have to cast the reference back to the type it was before if you want to call methods on the reference that are defined in the subclass.

Consider this example.



This will produce a compile-time error because no matter what reference type you send to equals, it will be widened to an Object reference.

The class Object does not define the method num().

So you can only call methods on o that are defined in Object.
 
Don't get me started about those stupid light bulbs.
 
subject: Casting Object References