Static methods in Java Interfaces?

[Rajiv Chelsea]

why can't we have static methods in an interface?

[Nicola Garofalo]

A static method is a method related to a class, not to an interface.
In interfaces you define a behaviour that has to be implemented by a class. How do you implement an interface? Overriding all the methods declared by that interface.
But static methods cannot even be overridden...

[Devaka Cooray]

Let's suppose that it was allowed.

public interface TestInterface{
  void doIt();
  static void printIt();
}

Now since printIt() is static, you may call to that method directly as:

TestInterface.printIt();

Now, what could be happen? printIt() has no body!
Fortunately, static methods are not allowed for interfaces.

[Abhijeet Ravankar]

Simplest explanation is that methods in interfaces are by default "abstract". And we cannot have abstract static methods.

But, I tried this code and it worked!!! (Can we really have static methods in interface!)

public interface CoolInterface
{
  public static final Runnable coolName = new java.lang.Runnable(){public void run(){System.out.println("static interface method alive!");}};
}

public class CoolClass implements CoolInterface
{
    public static void main (String args[] )
    {
        coolName.run();
    }
}

and you get output ... program runs! (umm... somebody please explain me too. I am also a bit confused.)

[Nicola Garofalo]

coolName is not a static method, is a static variable. All variables in interfaces are static public and final, i.e. they are constants.
You defined a constant, not a static method.

[Devaka Cooray]

Can we really have static methods in interface!

As Nicola said, what that interface has is a constant attribute named 'coolName' which refers to an object of an anonymous inner class that implements a Runnable interface.

[Rajiv Chelsea]

Hi Devaka

Suppose static methods were allowed in an interface. A class implements that interface , and in that class we would give d definition(body) for
the static method , as for normal interface methods. and then we could call the implemented method..

Why is the above not possible?

[Devaka Cooray]

Static methods cannot be *overridden* (you can hide them, though). Have a look at this this FAQ.

[Abhijeet Ravankar]

Yes, its just a constant attribute named 'coolName' which refers to an object of an anonymous inner class that implements a Runnable interface.

Thanks Devaka and Nicola for clearing.
Thanks Rajiv for asking interesting question.

[Rajiv Chelsea]

hi devaka

As your reply suggests...

Is implementing an interface method in a class, same as trying to override it?

[Devaka Cooray]

Rajiv Chelsea wrote:Is implementing an interface method in a class, same as trying to override it?

Of course