How to stop other apps playing music from my current activity?

AudioManager am = (AudioManager)getSystemService(Context.AUDIO_SERVICE);

// Request audio focus for playback
int result = am.requestAudioFocus(focusChangeListener,
// Use the music stream.
AudioManager.STREAM_MUSIC,
// Request permanent focus.
AudioManager.AUDIOFOCUS_GAIN);


if (result == AudioManager.AUDIOFOCUS_REQUEST_GRANTED) {
// other app had stopped playing song now , so u can do u stuff now .
}

Audio focus is assigned in turn to each application that requests it. This means that if another
application requests audio focus, your application will lose it. You will be notifi ed of the loss of
audio focus through the onAudioFocusChange handler of the Audio Focus Change Listener you
registered when requesting the audio focus

      private OnAudioFocusChangeListener focusChangeListener =
          new OnAudioFocusChangeListener() {
                  public void onAudioFocusChange(int focusChange) {
                             AudioManager am =(AudioManager)getSystemService(Context.AUDIO_SERVICE);
                    switch (focusChange) {

                           case (AudioManager.AUDIOFOCUS_LOSS_TRANSIENT_CAN_DUCK) :
                           // Lower the volume while ducking.
                           mediaPlayer.setVolume(0.2f, 0.2f);
                           break;
                           case (AudioManager.AUDIOFOCUS_LOSS_TRANSIENT) :
                           pause();
                           break;

                           case (AudioManager.AUDIOFOCUS_LOSS) :
                           stop();
                           ComponentName component =new ComponentName(AudioPlayerActivity.this,MediaControlReceiver.class);
                           am.unregisterMediaButtonEventReceiver(component);
                           break;

                           case (AudioManager.AUDIOFOCUS_GAIN) :
                           // Return the volume to normal and resume if paused.
                           mediaPlayer.setVolume(1f, 1f);
                           mediaPlayer.start();
                           break;
                           default: break;
}
}
};