How do I prevent the end of Android Studio activities when I go back?

package com.example.android.wearable.recipeassistant;
import android.app.Activity;
import android.media.MediaPlayer;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.SeekBar;
public class MusicSetting extends Activity {
    MediaPlayermp; // Object for Music Playback
    int pos; // when the playback stopped
    private Button bStart;
    private Button bPause;
    private Button bRestart;
    private Button bStop;
    Private SeekBar; // Sikbar indicating music playback location
    Boolean isPlaying = false; // variable to determine if it is playing
    class MyThread extends Thread {
        @Override
        Public void run() { // method called back when thread starts
            // Move the tickbar stick little by little (Repeat until the end of the song)
            while(isPlaying) {
                sb.setProgress(mp.getCurrentPosition());
            }
        }
    }
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.music_setting);
        sb = (SeekBar)findViewById(R.id.seekBar1);
        sb.setOnSeekBarChangeListener(new SeekBar.OnSeekBarChangeListener() {
            public void onStopTrackingTouch(SeekBar seekBar) {
                isPlaying = true;
                int ttt = seekBar.getProgress(); // where the user has moved
                mp.seekTo(ttt);
                mp.start();
                new MyThread().start();
            }
            public void onStartTrackingTouch(SeekBar seekBar) {
                isPlaying = false;
                mp.pause();
            }
            public void onProgressChanged(SeekBar seekBar,int progress,boolean fromUser) {
                if (seekBar.getMax()==progress) {
                    bStart.setVisibility(View.VISIBLE);
                    bStop.setVisibility(View.INVISIBLE);
                    bPause.setVisibility(View.INVISIBLE);
                    bRestart.setVisibility(View.INVISIBLE);
                    isPlaying = false;
                    mp.stop();
                }
            }
        });

        bStart = (Button)findViewById(R.id.button1);
        bPause = (Button)findViewById(R.id.button2);
        bRestart=(Button)findViewById(R.id.button3);
        bStop  = (Button)findViewById(R.id.button4);

        bStart.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // MediaPlayer object initialization, playing
                mp = MediaPlayer.create(
                        getApplicationContext(), // the controller of the current screen
                        R.raw.music); // music file
                mp.setLooping(false); // true:Repeat indefinitely
                mp.start(); // Start playing songs

                int a = mp.getDuration(); // Playtime of the song (miliSecond)
                sb.setMax(a);// set the maximum range of the check bar to the playback time of the song
                newMyThread().start(); // Start thread to draw check bar
                isPlaying = true; // Checkbar thread to repeat

                bStart.setVisibility(View.INVISIBLE);
                bStop.setVisibility(View.VISIBLE);
                bPause.setVisibility(View.VISIBLE);
            }
        });

        bStop.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // End of music
                isPlaying = false; // Thread termination

                mp.stop(); // stop
                mp.release(); // release resource
                bStart.setVisibility(View.VISIBLE);
                bPause.setVisibility(View.INVISIBLE);
                bRestart.setVisibility(View.INVISIBLE);
                bStop.setVisibility(View.INVISIBLE);

                sb.setProgress(0); // Checkbar initialization
            }
        });

        bPause.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // Pause
                pos = mp.getCurrentPosition();
                mp.pause(); // pause
                bPause.setVisibility(View.INVISIBLE);
                bRestart.setVisibility(View.VISIBLE);
                isPlaying = false; // Thread stop
            }
        });
        bRestart.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // Restart from where it stopped
                mp.seeTo(pos); // Move to Pause
                mp.start(); // Start
                bRestart.setVisibility(View.INVISIBLE);
                bPause.setVisibility(View.VISIBLE);
                isPlaying = true; // Change flag to play
                newMyThread().start(); // start thread
            }
        });
    } } // end of onCreate
    @Override
    protected void onPause() {
        super.onPause();
        isPlaying = false; // Thread stop
        if (mp!=null) {
            mp.release(); // release resource
        }
        bStart.setVisibility(View.VISIBLE);
        bStop.setVisibility(View.INVISIBLE);
        bPause.setVisibility(View.INVISIBLE);
        bRestart.setVisibility(View.INVISIBLE);
    }
}