Example OnAudioFocusChangeListener

private AudioManager.OnAudioFocusChangeListener mOnAudioFocusChangeListener;
//…
mOnAudioFocusChangeListener = new AudioManager.OnAudioFocusChangeListener() {
 
			@Override
			public void onAudioFocusChange(int focusChange) {
				switch (focusChange) {
				case AudioManager.AUDIOFOCUS_GAIN:
					Log.i(TAG, "AUDIOFOCUS_GAIN");
                                  // Set volume level to desired levels
					play();
					break;
				case AudioManager.AUDIOFOCUS_GAIN_TRANSIENT:
					Log.i(TAG, "AUDIOFOCUS_GAIN_TRANSIENT");
                                  // You have audio focus for a short time
                                  play();
					break;
				case AudioManager.AUDIOFOCUS_GAIN_TRANSIENT_MAY_DUCK:
					Log.i(TAG, "AUDIOFOCUS_GAIN_TRANSIENT_MAY_DUCK");
                                  // Play over existing audio
                                  play();
					break;
				case AudioManager.AUDIOFOCUS_LOSS:
					Log.e(TAG, "AUDIOFOCUS_LOSS");
					stop();
					break;
				case AudioManager.AUDIOFOCUS_LOSS_TRANSIENT:
					Log.e(TAG, "AUDIOFOCUS_LOSS_TRANSIENT");
                                  // Temporary loss of audio focus - expect to get it back - you can keep your resources around
					pause();
					break;
				case AudioManager.AUDIOFOCUS_LOSS_TRANSIENT_CAN_DUCK:
					Log.e(TAG, "AUDIOFOCUS_LOSS_TRANSIENT_CAN_DUCK");
                                  // Lower the volume
					break;
				}
			}
		};

Requesting Audio Focus

AudioManager am = (AudioManager) mContext
					.getSystemService(Context.AUDIO_SERVICE);
			// Request audio focus for play back
			int result = am.requestAudioFocus(mOnAudioFocusChangeListener,
			// Use the music stream.
					AudioManager.STREAM_MUSIC,
					// Request permanent focus.
					AudioManager.AUDIOFOCUS_GAIN);
 
			if (result == AudioManager.AUDIOFOCUS_REQUEST_GRANTED) {
				mAudioFocusGranted = true;
			} else if (result == AudioManager.AUDIOFOCUS_REQUEST_FAILED) {
                         // take appropriate action
                     }

Thank you very much, but I have a question hope you can help me.
How do I control headphone button for play, pause or next, prev music?

I know that it's too late, but somebody else could need the hint, you should use MediaSessionCompat in order to control your player from headphone buttons, Google Assistant etc...

thanks a lot
You r saving my times

Thank you more than very much!
This code snipet saved my day on studying how to manipulate audio focus! 'Cause there were tons os codes where I couldn't ser how to conect my listener in...
I really appreciated!