Inner Class Doubt

[Abhi vijay]

Source: Devaka Cooray's Exam Simulator

 import java.io.*;
 
class A{}
class B extends A{}
class C extends A implements Serializable{}
final class D extends B{}
 
public class Refcast{
     public static void main(String args[]){
          A a=new A();
          B b=new B();
          C c=new C();
          D d=new D();
          Object ob=c; //Line-1
          d=(D)ob; //Line-2
          d=(D)new B(); //Line-3
          c=(C)new Serializable(){}; //Line-4
     }
}   

I am not able to understand why Line-4 is generating a compiler error?

[Ruben Soto]

Abhi, when you create the anonymous class instance it can only pass the Is-A test for Serializable, so the compiler will catch that it can never be cast to C. You could do it the other way around though (I think, you can try this and see if it works)

Serializable s = (Serializable) new C(){};

In this case, the instance of the anonymous class would pass the Is-A test for C, which itself passes the Is-A test for Serializable, so the cast would both compile and run.
[ December 28, 2008: Message edited by: Ruben Soto ]

[Punit Singh]

This happends as Anonymous class has no syntax to say it extends C implements Serializable.

class C_serializable extends C implements Serializable{
}

Above case is not possible in case of anonymous class, compiler can see this, will find that in

c=(C)new Serializable(){}; //Line-4

this scenario there is no way that this innerclass could be a child of class C.