java.lang.ClassException: A cannot be cast into B

Question

I implemented this code:

class A {
    //some code
}
class B extends A {
    // some code
}

class C {
    public static void main(String []args)
    {
              


        

Answer 1

Following is a compiletime casting -

A a = new B();

Such static castings are implicitly performed by the compiler, because the compiler is aware of the fact that B is-a A.

Following doesn't compile -

B b = new A();

No compiletime casting here because the compiler knows that A is not B.

Following compiles -

B b = (B) new A();

It is a dynamic casting. With (B) you are telling the compiler explicitly that you want the casting to happen at runtime. And you get a CCE at runtime, when the runtime tries to perform the cast but finds out that it cannot be done and throws a CCE.

When you do (or have to do) something like this, the responsibility falls upon you (not the compiler) to make sure that a CCE doesn't occur at runtime.