Question

I made an Interface having all common methods a player should have. I implemented it in my code, my colleague too. But many of the developers who were not aware with my interface created their own methods like playMyPlayer() etc.

How can I force other programmers to implement my interface ?

Answer 1

Explaning with your own scenario:

Interface

interface Player{
    public void play();
    public void pause();
    public void stop();
}

Classes which are implementing Player Intreface;

class AudioPlayer implements Player{...}

class VideoPlayer implements Player{...}

Some extra class. Meaningless but seems relevant

Class PlayList{}

An enum who plays important role;

enum MEDIAPLAYER {
    AUDIO,VIDEO;

    public Player getPlayer() {
        switch (this) {
            case AUDIO:
                return new AudioPlayer();
            case VIDEO:
                return new VideoPlayer();
            default:
                return new AudioPlayer();
        }
    }
}

Using your code

Player testPlayer = MEDIAPLAYER.getPlayer();
:
testPlayer.play();

Now if any new player is added, its entry will go to MEDIAPLAYER which is returning Player type object. So everyone would have to implement Player

Another approach:

You can create an abstract class, say MasterPlayer, who is having all the abstract methods Player interface has. In addition, MasterPlayer will have some additional methods like managing PlayList