请教ActionListener问题

Tor_Jens

偶在编一个java程序时，用到actionlistener这个interface. 代码如下：
private class CreatureListener implements ActionListener
   {
      //--------------------------------------------------------------
      //  Updates the position of the image and possibly the direction
      //  of movement whenever the timer fires an action event.
      //--------------------------------------------------------------
      public void actionPerformed (ActionEvent event)
      {
       x = generator.nextInt(1000);
       y = generator.nextInt(800);
       repaint();
      }
偶不明白为什么它有UPDATE功能，也就是说当程序运行时图片的位置可以连续不断的改变。如果只看程序，我觉得只产生一个随机的位置程序就终止了。
请高手指教，先谢了！！！

猫小

The listener interface for receiving action events. The class that is interested in processing an action event implements this interface, and the object created with that class is registered with a component, using the component's addActionListener method. When the action event occurs, that object's actionPerformed method is invoked.