about interface Casting

[abhijit Ohal]

 
class A{}
class B extends A implements E{}//line 1
class C extends A{}
class D extends B{}
interface E{}
public class Question07 {
public static void main(String[] args) {
A a = new D();//line 2
C c = new C();//line 3
E e = (E)a;//line 4
B b = (B)e;//line 5
}
}

Can some one explain E e = (E)a;//line 4
how it works as E is interface

Also if did something

 
A a = new A(); 
E e =  (E) a;  

it didn't give any compilation error but give run time
Please explain any more combinations too.

[Neelesh Bodas]

You can always cast an object to any interface. If the static type of the object being casted is not a final class then this cast doesnot fail at compile time.

[wise owen]

Casting to an Interface is ALWAYS OK?