If I call an interface method, will it get the method body from implementation class and execute?

Question

I have an interface Interface1. I have its implementation Imple implements Interface1 (all methods have been implemented :) ).

Now, consider a third class CheckCall, can I do a call in the class CheckCall like I mention below :

Interface1 interface1;
interface1.method();

All necessary imports have been done. Please tell me is it possible or not , if not then ok and if yes, then tell me what will happen if I've more than one implementing classes for the same interface and I'm doing the same call.

Answer 1

Sure, your code works fine! You just have to initialize your variable interface1 with an actual implementation (i.e. new Imple()).

Check out this example, I used your class-names:

public class CheckCall {

    interface Interface1 {
        void method();
    }

    static class Imple implements Interface1 {
        @Override
        public void method() {
            System.out.println("Imple.method1()");
        }
    }

    public static void main(String[] args) {
        Interface1 interface1;
        interface1 = new Imple();
        interface1.method();
    }

}

Answer 2

Well, you cannot call the method directly on the interface, but you can do what you wrote, more or less.

You wrote:

Interface1 interface1;
interface1.method();

This will work if you do this:

Interface1 interface1 = new CheckCall();
interface1.method();

then tell me what will happen if i have more than one impl classes for the same interface and i am doing the same call

Well, that's the nice thing about Java: the problem you're referring to is called the "diamond problem":

http://en.wikipedia.org/wiki/Diamond_problem

And it doesn't really exist in Java because Java fully supports multiple inheritance, but only through "multiple (Java) interface inheritance" (* see comment).

So in your case when you call interface1.method() you're either calling Impl's method or CheckCall's method and there's no confusion possible.