public class MyTestService extends Service {
  
  public class TestBinder extends Binder {
    MyTestService getService() {
        return MyTestService.this;
    }
  }
  
  
  @Override
  public IBinder onBind(Intent intent) {
    return mBinder;
  }
  
  
  private final IBinder mBinder = new TestBinder();  
  
}


// Подключение к сервису

..........................................

private MyTestService mBoundService;

void doBindService() {
  private ServiceConnection mConnection = new ServiceConnection() {
    public void onServiceConnected(ComponentName className, IBinder service) {
        mBoundService = ((MyTestService.TestBinder)service).getService(); // Здесь service приводится к MyTestService.TestBinder
    }

    public void onServiceDisconnected(ComponentName className) {
        mBoundService = null;
    }
  };

    bindService(new Intent(this, 
            MyTestService.class), mConnection, Context.BIND_AUTO_CREATE);
    mIsBound = true;
}