anonymous (unnamed) Classes by default always folllows Overriding concept

[Mahendra Athneria]

hi all,

my question is related to anonymous (unnamed) classes.
Anonymous classes are always sub-class of the some "new ClassName()". so my question is that if it is always sub-class of some class and if it is define the method that is already defined in super class then it is overriding the method. or we can say that it is by default follow the overriding principle.

I need your thoughts on this Topic.

Example Attached from SCJP Kathy Siera Book.

class Popcorn {
public void pop() {
System.out.println("popcorn");
}
}
class Food {
Popcorn p = new Popcorn() {
public void pop() {
System.out.println("anonymous popcorn");
}
};
}

The Popcorn reference variable refers not to an instance of Popcorn, but to an
instance of an anonymous (unnamed) subclass of Popcorn.
Let's look at just the anonymous class code:

2. Popcorn p = new Popcorn() {
3. public void pop() {
4. System.out.println("anonymous popcorn");
5. }
6. };

Regards,
Mahendra Athneria
Mumbai- India


[Nitesh: Added code tags. Please UseCodeTags]

[Campbell Ritchie]

Yes, they follow the rules of overriding and polymorphism: remember new fields or new static members count as hiding rather than overriding.

But your anonymous classes are in fact instances of the Popcorn class. Try executing this enhancement of the class you quoted

import static java.lang.System.out;

public class Popcorn
{
    public void pop()
    {
        out.println("Ordinary popcorn");
    }//end pop
    
    private void go()
    {
        Popcorn p = new Popcorn();
        p.pop();
        out.printf("p instanceof Popcorn: %b, p.getClass().getName(): %s%n",
                p instanceof Popcorn, p.getClass().getName());
        Popcorn pp = new Popcorn()
        {
            @Override
            public void pop()
            {
                out.println("Extraordinary popcorn");
            }//end pop method
        };//end anonymous inner class
        out.printf("pp instanceof Popcorn: %b, pp.getClass().getName(): %s%n",
                pp instanceof Popcorn, pp.getClass().getName());
        pp.pop();
        Popcorn ppp = new Popcorn()
        {
            @Override
            public void pop()
            {
                out.println("Much better popcorn");
            }//end pop method
        };//end anonymous inner class
        ppp.pop();
        out.printf("ppp instanceof Popcorn: %b, ppp.getClass().getName(): %s%n",
                ppp instanceof Popcorn, ppp.getClass().getName());
    }//end go
    
    public static void main(String[] args)
    {
        new Popcorn().go();
    }//end main
}//end class

That demonstrates whether your Popcorn objects are instances of Popcorn, and what the class names are, and that you are in fact overriding the pop method. Because you cannot access the class name you cannot do a class cast on pp or ppp, so you cannot add methods.

And please maintain indentation inside the code tags.

[Mahendra Athneria]

Thanks for your Answer.

I have one more question related to overriding and implementation.

Yesterday i faced one problem. i declared one interface with some functions. then i created implementer class who implement the interface. while implementing the methods i used @Override annotations. when i compiled then it gives error

method does not override a method from its superclass @Override

but i am overriding the method, and if i am overriding the method then why cant i use @Override annotations?

Thanks in Advance

[Campbell Ritchie]

That is strictly speaking correct; you are not overriding an interface method, but implementing it.
If you use the compiler from Java6, it won't give that error message.