Main Activity of the Slot Machine

MainActivity.java

public class MainActivity extends AppCompatActivity {

 private TextView msg;
 private ImageView img1, img2, img3;
 private Wheel wheel1, wheel2, wheel3;
 private Button btn;
 private boolean isStarted;

 public static final Random RANDOM = new Random();

 public static long randomLong(long lower, long upper) {
   return lower + (long) (RANDOM.nextDouble() * (upper - lower));
 }

 @Override
 protected void onCreate(Bundle savedInstanceState) {
   super.onCreate(savedInstanceState);
   setContentView(R.layout.activity_main);
   img1 = (ImageView) findViewById(R.id.img1);
   img2 = (ImageView) findViewById(R.id.img2);
   img3 = (ImageView) findViewById(R.id.img3);
   btn = (Button) findViewById(R.id.btn);
   msg = (TextView) findViewById(R.id.msg);

   btn.setOnClickListener(new View.OnClickListener() {
     @Override
     public void onClick(View view) {
     if (isStarted) {
       wheel1.stopWheel();
       wheel2.stopWheel();
       wheel3.stopWheel();

       if (wheel1.currentIndex == wheel2.currentIndex && wheel2.currentIndex == wheel3.currentIndex) {
         msg.setText("You win the big prize");
       } else if (wheel1.currentIndex == wheel2.currentIndex || wheel2.currentIndex == wheel3.currentIndex
         || wheel1.currentIndex == wheel3.currentIndex) {
         msg.setText("Little Prize");
       } else {
         msg.setText("You lose");
       }

       btn.setText("Start");
       isStarted = false;

     } else {

       wheel1 = new Wheel(new Wheel.WheelListener() {
         @Override
         public void newImage(final int img) {
           runOnUiThread(new Runnable() {
             @Override
             public void run() {
               img1.setImageResource(img);
             }
           });
         }
       }, 200, randomLong(0, 200));

       wheel1.start();

       wheel2 = new Wheel(new Wheel.WheelListener() {
         @Override
         public void newImage(final int img) {
           runOnUiThread(new Runnable() {
             @Override
             public void run() {
               img2.setImageResource(img);
             }
           });
         }
       }, 200, randomLong(150, 400));

       wheel2.start();

       wheel3 = new Wheel(new Wheel.WheelListener() {
         @Override
         public void newImage(final int img) {
           runOnUiThread(new Runnable() {
             @Override
             public void run() {
               img3.setImageResource(img);
             }
           });
         }
       }, 200, randomLong(150, 400));

       wheel3.start();

       btn.setText("Stop");
       msg.setText("");
       isStarted = true;
     }
   }
  });
 }
}