/** Constructor creates and starts the timer. */
  public JumpOnEnemyExample() {
    KeyListener listener = new MyKeyListener();
    this.addKeyListener(listener);
    timer = new Timer(interval, new TimerAction());

    Renderer r = new SolidRenderer(Color.GREEN);
    platform = new Platform(100, 300, 400, 20, r);

    r = new SolidRenderer(Color.RED);
    Enemy e = new Enemy(200, 300 - SIZE, SIZE, SIZE, r);
    e.setBounds(200, 300);
    e.setDirection(1, 0);
    platform.addChild(e);

    r = new SolidRenderer(Color.YELLOW);
    player = new Projectile(100, 300 - SIZE, SIZE, SIZE + SIZE / 2, r);

    timer.start();
  }