Can we Pass Abstract Class Object as Argument Using Polymorphism?

Question

I have a class with name 'A'. A is an abstract class. And class 'B' extends class 'A'.

And I have another class 'C'. In class 'C' there's a function with name show().

I want to pass an object of class 'A' which is abstract. Is it possible?

Or

Can we do this using Polymorphism.

If yes! then How?

@ZartashZulfiqar Why can't you stick to the rules of the language. You can't instantiate an abstract class. Period. — Chetan Kinger, Jul 13 '15 at 10:49
you can do this. A a = new B(); is this what you are looking for? — Anant Laxmikant Bobde, Jul 13 '15 at 10:51
you can define your method as `show(A a)` ad it will accept everything which extends type `A`. is that what you are looking for? — user902383, Jul 13 '15 at 10:53
Not just is it possible, it is recommended. It is what [programming to an interface](http://stackoverflow.com/questions/383947/what-does-it-mean-to-program-to-an-interface) is about. — Raedwald, Jul 13 '15 at 11:38

score 4 · Answer 1 · answered Jul 13 '15 at 10:58

I want to pass an object of class 'A' which is abstract. Is it possible?

Yes, it is. The following is valid:

abstract class A {}

class B extends A {}

class C {
    public void show(A a) {}
}

Even though A is abstract, you can receive parameters of type A (which, in this case, would be objects of type B).

You cannot really pass an object of class A, though, since A is abstract and cannot be instantiated.

Can we do this using Polymorphism.

The above example actually already used polymorphism (subtyping).

https://en.wikipedia.org/wiki/Polymorphism_(computer_science)#Subtyping

score 3 · Accepted Answer · edited Dec 17 '19 at 12:00

Pretty much the same as above answer, just elaborated with code. Naive way of telling, you cannot have abstract class name next to new operator except in case with array, as in A a[] = new A[10]; where you have still allocate Objects of concrete class for each element in Array.

abstract class A{
        abstract void tell();
}

class B extends A{
        void tell(){
                System.out.println("I am B Telling");
        }
}

public class Test{

        public static void whoTold(A a)
        {
                a.tell();
        }

        public static void main(String[] args){
                B b = new B();
                whoTold(b);
       }
}

Can we Pass Abstract Class Object as Argument Using Polymorphism?

2 Answers2