Repaint轨迹保留？（待处理，待编辑）

 import java.awt.Color;
 import java.awt.Graphics;

 import javax.swing.JFrame;
 import javax.swing.JPanel;

 public class SimpleAnimation {

     /**
      * @param args
      */
     int x=0,y=0;
     public static void main(String[] args) {
         // TODO Auto-generated method stub
         SimpleAnimation gui=new SimpleAnimation();
         gui.test();
     }
     public void test() {
         JFrame frame=new JFrame();
         frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

         MyDrawPanel drawPanel=new MyDrawPanel();

         frame.getContentPane().add(drawPanel);
         frame.setSize(500, 500);
         frame.setVisible(true);

         for (int i = 0; i < frame.getHeight()-60; i++) {
             x++;
             y++;
             drawPanel.repaint();
             try {
                 Thread.sleep((int)(Math.random()*140));
             } catch (Exception ex) {
                 // TODO: handle exception
                 ex.printStackTrace();
             }
         }
     }
     class MyDrawPanel extends JPanel{
         public void paintComponent(Graphics g) {
             int red=(int)(Math.random()*255);
             int green=(int)(Math.random()*255);
             int blue=(int)(Math.random()*255);
             g.setColor(Color.red);
             g.fillRect(0, 0, this.getWidth(), this.getHeight());
             g.setColor(new Color(red,green,blue));
             g.fillOval(x, y, 40, 40);
         }
     }

 }