Why superclass invokes the subclass's overridden method?

Question

I have two classes, Parent (superclass) and Child (subclass).

public class Parent(){

   public void hello(){
       System.out.println("HelloParent");
       bye();
   }

   public void bye(){
       System.out.println("ByeParent");
   }
}

public class Child extends Parent(){

   @Override
   public void hello(){
       super.hello();
   }

   @Override
   public void bye(){
       System.out.println("ByeChild");
   }
}

If I create a Child instance and invoke its hello() method, it invokes the Child 's hello method, and not the Parent 's hello method.

Child c = new Child();
c.hello();

Output:

"HelloParent"
"ByeChild"

But why is it not "ByeParent"?

Why doesn't it invoke the superclass's method?

Answer 1

Any instance method call will happen on the object the instance belong to no matter where the code is. So while executing this code:

 public void hello(){
       System.out.println("HelloParent");
       bye();
   }

bye method will be called on the the calling object ie Child and hence Child method is called.

Answer 2

Well, that is how polymorphism works in OO. Since the instance you are working with is Child , it is no surprise that Child.bye() was invoked!

If you really wanted it to print ByeParent , then you'd have to write the bye() in Child as follows:

@Override
public void bye(){
    super.bye();
    System.out.println("ByeChild");
}

Note that you could've also done this:

Parent obj = new Child();
obj.hello();

However, even in this case, it would still print ByeChild .

Answer 3

Overriding a method replaces it completely, it doesn't add on to it. If you also want to call the original method, you need to call it explicitly using the keyword "super":

@Override
public void bye(){
    super.bye();
    System.out.println("ByeChild");
}