Question

Suppose I have class A

public class A
{
    public void method()
    {
        //do stuff
    }
}

Also another class B

public class B extends A
{
    public void method()
    {
        //do other stuff
    }
}

Now I have the following statements:

A a = new B();
a.method();

Is this an example of run time polymorphism? If yes, then is no binding is done for the reference a at compile time?

Answer 1

The compiler will tell you that this can’t work, because there’s no relationship between A and B that will allow you to write A a = new B();

B either has to extend A or both have to implement a common interface with void method() in it.

You could have answered this very quickly by trying it with the compiler. Be an experimentalist – it’s faster than forums.

UPDATE:

It works, now that B extends A. The binding that you care about, dynamic binding, is done at runtime. The static compile time type for the variable “a” is class A; at runtime it is dynamically bound to a reference of type B. Yes, I would consider this to be an example of polymorphism.