Android Studio and mediaPlayer

float volume = 0;

private void startFadeIn(){
    final int FADE_DURATION = 3000; //The duration of the fade
    //The amount of time between volume changes. The smaller this is, the smoother the fade
    final int FADE_INTERVAL = 250;
    final int MAX_VOLUME = 1; //The volume will increase from 0 to 1
    int numberOfSteps = FADE_DURATION/FADE_INTERVAL; //Calculate the number of fade steps
    //Calculate by how much the volume changes each step
    final float deltaVolume = MAX_VOLUME / (float)numberOfSteps;

    //Create a new Timer and Timer task to run the fading outside the main UI thread
    final Timer timer = new Timer(true);
    TimerTask timerTask = new TimerTask() {
        @Override
        public void run() {
            fadeInStep(deltaVolume); //Do a fade step
            //Cancel and Purge the Timer if the desired volume has been reached
            if(volume>=1f){
                timer.cancel();
                timer.purge();
            }
        }
    };

    timer.schedule(timerTask,FADE_INTERVAL,FADE_INTERVAL);
}

private void fadeInStep(float deltaVolume){
    mediaPlayer.setVolume(volume, volume);
    volume += deltaVolume;

}

**Audio track #1 is playing but coming to the end**
startFadeOut();
mediaPlayer.stop();
mediaPlayer.reset();
mediaPlayer.setDataSource(context,audiofileUri);
mediaPlayer.prepare();
mediaPlayer.start();
startFadeIn();
**Audio track #2 has faded in and is now playing**

public class MainActivity extends AppCompatActivity {

private MediaPlayer mediaPlayer;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    mediaPlayer = MediaPlayer.create(this, R.raw.diwali);

    Button play = (Button) findViewById(R.id.play);
    play.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            mediaPlayer.start();
            mediaPlayer.setOnCompletionListener(new MediaPlayer.OnCompletionListener(){
                @Override
                public void onCompletion(MediaPlayer mp) {
                    Toast.makeText(MainActivity.this, "I'm done!", Toast.LENGTH_SHORT).show();
                }

            });
        }
    });

    Button pause = (Button) findViewById(R.id.pause);
    pause.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            mediaPlayer.pause();
        }
    });
}

<Button
    android:id="@+id/play"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@string/play" />

<Button
    android:id="@+id/pause"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@string/pause" />

MediaPlayer mp = MediaPlayer.create( getActivity() , R.raw.alphabetlist );

MediaPlayer mp; 
public View onCreateView(LayoutInflater inflater, ViewGroup container,
    Bundle savedInstanceState) {

    mp=MediaPlayer.create(getActivity(), R.raw.alphabetlist); 
    mp.start():  

    return inflater.inflate(R.layout.fragment_alphabet, container, false);
}

//just initialize inside ClickListener, speak_rost, and after .setOnCompletionListener, I put speak_rost().start; that was ALL, very nice problem, now all my 50+ buttons/layouts are "in the right form" to play 100+ time, every time I needed. Thank you.
layoutRost.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {


                speak_rost = MediaPlayer.create(hundred.this, R.raw.asa);
                speak_rost .setOnCompletionListener(new MediaPlayer.OnCompletionListener() {
                    public void onCompletion(MediaPlayer mysound) {
                        mysound.release();
                    }

                });
                speak_rost .start();
            }
        });