如何实现Swing容器组件的显示效果

/**   * 淡入淡出式显示内容组件的容器   * @author William Chen   */  public class GlassBox extends JComponent implements ActionListener{      //常数定义      private static final int ANIMATION_FRAMES=50;      private static final int ANIMATION_INTERVAL=10;      //帧索引      private int frameIndex;      //时钟      private Timer timer;           /** Creates a new instance of GlassBox */      public GlassBox() {      }           public void paint(Graphics g){          if(isAnimating()){              //根据当前帧显示当前透明度的内容组件              float alpha=(float)frameIndex/(float)ANIMATION_FRAMES;              Graphics2D g2d=(Graphics2D)g;              g2d.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_OVER, alpha));              //Renderer渲染机制              super.paint(g2d);          }else{              //如果是***次，启动动画时钟              frameIndex=0;              timer=new Timer(ANIMATION_INTERVAL, this);              timer.start();          }      }      //判断当前是否正在进行动画      private boolean isAnimating(){          return timer!=null && timer.isRunning();      }      //关闭时钟，重新初始化      private void closeTimer() {          if(isAnimating()){              timer.stop();              frameIndex=0;              timer=null;          }      }      //动画时钟处理事件      public void actionPerformed(ActionEvent e) {          //前进一帧          frameIndex++;          if(frameIndex>=ANIMATION_FRAMES)              //***一帧，关闭动画              closeTimer();          else//更新当前一帧              repaint();      }  }