How casting is done in this example

[Supriya Nimakuri]

what is the putput and why

class Base {}
class Sub extends Base {}
class Sub2 extends Base {}
public class CEx{
public static void main(String argv[]){
Base b=new Base();
Sub s=(Sub) b;
}
}

1) Compile and run without error
2) Compile time Exception
3) Runtime Exception


Regards

[Keith Lynn]

Originally posted by Supriya Nimakuri:
what is the putput and why

class Base {}
class Sub extends Base {}
class Sub2 extends Base {}
public class CEx{
public static void main(String argv[]){
Base b=new Base();
Sub s=(Sub) b;
}
}

1) Compile and run without error
2) Compile time Exception
3) Runtime Exception


Regards

At compile-time, a cast to a subclass is allowed.

However, at runtime, you can't cast a reference to a Base object to a reference to a Sub object.

A Base object is not a Sub object.

[Naseem Khan]

Base b=new Base();
Sub s=(Sub) b;

your code compiles fine as there is an inheritance relationship between the two i.e., between the type of b and Sub class. No matter who is super class of whom?

At runtime, b actually point to an instance of Base so can't be casted to any Subclass.
It can only be casted to Base or superclass of Base like Object.

So correct answer is...

2) Compile time Exception

which is ClassCastException at runtime.


Naseem
[ June 28, 2006: Message edited by: Naseem Khan ]