ClassCastException

Question

i have two classes in java as:

class A {

 int a=10;

 public void sayhello() {
 System.out.println(\"class A\");
 }
}

class B extends A {

 int a=20;

 pub         


        

Answer 1

This happens because the compile-time expression type of new A() is A - which could be a reference to an instance of B, so the cast is allowed.

At execution time, however, the reference is just to an instance of A - so it fails the cast. An instance of just A isn't an instance of B. The cast only works if the reference really does refer to an instance of B or a subclass.