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);
        }
    }

}