casting problem

[Dan Andrei]

given the code:
class X{}
class A extends X implements T{
public void foo(){
System.out.println("it works");
}
}
class B extends A{}
interface T{void foo();}
class BB{}
....
BB bb=new BB()
//T t=(T)bb;// runtime exception is OK -case A
B b=new B();// Case B
t=(T)b;
In case A the program gives a runtime exception no problem since object pointed by bb does not implement T
I think it should also give a runtime exception in Case B the object to which b points also does not implement interface T.
I do not understand why the program runs in this case.
I think the fact that class A which is a superclass of B and implements T
CANNOT be the explanation because.
JLS 2.0 states that the class itself must implement the interface
Can someone give me some input on this...

[Sudhakar Krishnamurthy]

Dan,
Your understanding is correct the code compiles because the parent class of B has already implemented the interface T.
Now think of this all public members of class A are members of class B so from the point of class B it really doesn't matter if the parent class has implemented the method as long as class B is aware of the method.
hope this helps.
-S

[Dan Andrei]

I used the same reasoning as you regarding the inheritance BUT
I thought the implements clause is mandatory, but it seems is not I just try an example and it compiles fine