How can I use different subclass in different situation?

Question

I have a dilemma like this:

I have parent class MediaPlayer, then some subclass extends from it, let's say they are MediaPlayerSub1 MediaPlayerSub2 MediaPlayerSub3, all of they extend some differnt methods.

In my client, I want use different subclass in different situation, so I am faced with difficulties: when I use MediaPlayer I always need to judge which subclass it is, for example:

MediaPlayer mMediaPlayer = initPlayer()
// ... do some operation from MediaPlayer

// ... do operation from sub class
if (mMediaPlayer instanceof MediaPlayerSub1) {
    mMediaPlayer = (MediaPlayerSub1)mMediaPlayer;
    // ... do operation from MediaPlayerSub1
} else if (mMediaPlayer instanceof MediaPlayerSub2) {
    mMediaPlayer = (MediaPlayerSub2)mMediaPlayer;
    // ... do operation from MediaPlayerSub2
} else if (mMediaPlayer instanceof MediaPlayerSub3) {
    mMediaPlayer = (MediaPlayerSub3)mMediaPlayer;
    // ... do operation from MediaPlayerSub3
}

Do I have better choice to refactor the code to reduce the coupling?

Answer 1

If you are the author of MediaPlayer you can just write an abstract method in MediaPlayer

abstract void action();

and override it in each of the subclasses, like this:

@Override
void action() {
   // do something
}

Then you just need to call mMediaPlayer.action().

If you are not the author of MediaPlayer you can do the same thing but using wrapper classes, like this

abstract class MediaPlayerWrapper {

    private final MediaPlayer mediaPlayer;

    MediaPlayerWrapper(MediaPlayer mediaPlayer) {
       this.mediaPlayer = mediaPlayer;
    }

    MediaPlayer getMediaPlayer() {
        return mediaPlayer;
    }

    abstract void action();
}

Then you create subclasses for each subclass of MediaPlayer. Like this:

final class MediaPlayerWrapper1 extends MediaPlayerWrapper {       

    MediaPlayerWrapper1(MediaPlayerSub1 mediaPlayer) {
        super(mediaPlayer);
    }

    @Override 
    public void action() {
        // do stuff with the MediaPlayer. You will need to call getMediaPlayer() first.
    }
}

Then you just need to use a MediaPlayerWrapper instead of a MediaPlayer.