Inheritance and polymorphism - understanding

Question

I have a class A and class B which extends A and is a subclass. Now i have

A aObject = new A(); and
A bObject = new B();

Now can i call the method in class B which is not in A using bObject without typecasting ?

If we cant do so without typecasting, what is the advantage of polymorphism then?

Thanks.

Answer 1

No, you definitely need to cast bObject to B.

This is because, as far as the compiler is concerned, bObject is of the declared class A. Imagine that instead of using a constructor, you had returned bObject from a function which returns class A..... how could the compiler possibly know that it is actually of class B?

You therefore need to do a runtime cast or instanceof check before the compiler will let you use it as class B.

Answer 2

No, you cannot. On both objects aObject and bObject you can call only methods that are defined for A without using casting.

If you defined bObject to be of type B, then you could, but as your code stands you can only work with A's methods and members.