Subclassing and overriding methods

Question

I have class A and class B which extends A.

class A {

    public void play(){
      System.out.println("A"):
    }
}

class B extends A {
    @Override
    public void play(){
      System.out.println("B"):
    }
}

Lets say I have something like that:

 A myObj = new B();
 ((A)myObj).play;

This is still show B in the system out. Shouldn't it show A since I upcasted it and I executed play. How can I call the super play given that my object is of type B?

Nope. That's not how Java works. – Matt Ball Apr 01 '14 at 04:14 — Matt Ball, Apr 01 '14 at 04:14

score 2 · Accepted Answer · answered Apr 01 '14 at 04:15

2

Casting a reference does not change the underling object.

myObj is a variable that stores a reference to an A object. In your code, that object is a B.

When you cast myObjt to a B you're narrowing the reference to a subclass so that you can invoke one of its methods. This does nothing to the B object.

answered Apr 01 '14 at 04:15

Sotirios Delimanolis

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So is there a way I can the super method? If not I guessI have to put some logic in the subclass play to call the higher one – Snake Apr 01 '14 at 04:16
2

@Snake You can't from the calling code. You can do it within the `B` methods with the `super` keyword. – Sotirios Delimanolis Apr 01 '14 at 04:17

Dawood ibn Kareem · Answer 2 · 2014-04-01T07:43:09.820

1

The cast is irrelevant. The whole point of polymorphism is that the version of the method that gets called depends on the class of the object (that is, what it was created as), and not on the type of the referring expression (that is, what it was declared as or cast to).

edited Apr 01 '14 at 07:43

answered Apr 01 '14 at 04:23

Dawood ibn Kareem

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score 0 · Answer 3 · answered Apr 01 '14 at 04:21

0

((A)myObj) is not doing nothing here, no point casting integer to integer.

Also typecasting doesnt change object reference.

answered Apr 01 '14 at 04:21

Vinay Pandey

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Subclassing and overriding methods

3 Answers3

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