关于JAVA绘图双缓冲技术

Question

package two;

import java.awt.Color;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.Rectangle;

import javax.swing.JFrame;

public class G1P2 extends JFrame{
final int WIDTH = 900,HEIGHT = 650;

double p1Speed = 0.5,p2Speed=0.5;
Rectangle left = new Rectangle(0,0,WIDTH/9,HEIGHT);
Rectangle right = new Rectangle((WIDTH/9)*9,0,WIDTH/9,HEIGHT);
Rectangle top  = new Rectangle(0,0,WIDTH,HEIGHT/9);
Rectangle bottom = new Rectangle(0,(HEIGHT/9)*9,(WIDTH/9)*10,HEIGHT/9);
Rectangle center = new Rectangle((int)((WIDTH/9)*2.5),(int)((HEIGHT/9)*2.5),(int)((WIDTH/9)*5),(HEIGHT/9)*4);

Rectangle obstacle = new Rectangle(WIDTH/2,(int)((HEIGHT/9)*7),WIDTH/10,HEIGHT/9);
Rectangle obstacle2 = new Rectangle(WIDTH/3,(int)((HEIGHT/9)*5),WIDTH/10,HEIGHT/4);
Rectangle obstacle3 = new Rectangle(2*(WIDTH/3),(int)((HEIGHT/9)*5),WIDTH/10,HEIGHT/4);
Rectangle obstacle4 = new Rectangle(WIDTH/3,(int)(HEIGHT/9),WIDTH/30,HEIGHT/9);
Rectangle obstacle5 = new Rectangle(WIDTH/2,(int)((HEIGHT/9)*1.5),WIDTH/30,HEIGHT/4);

Rectangle finish = new Rectangle(WIDTH/9,(HEIGHT/2)-HEIGHT/9,(int)((HEIGHT/9)*1.5),HEIGHT/70);

Rectangle p1 = new Rectangle(WIDTH/9,HEIGHT/2,WIDTH/30,WIDTH/30);
Rectangle p2 = new Rectangle(((WIDTH/9)+(int)((WIDTH/9)*1.5)/2),(HEIGHT/2)+(HEIGHT/10),WIDTH/30,WIDTH/30);

Rectangle lineO = new Rectangle(WIDTH/9,HEIGHT/2,(int)((WIDTH/9)*1.5)/2,HEIGHT/140);
Rectangle lineI = new Rectangle(((WIDTH/9)+((int)((WIDTH/9)*1.5)/2)),(HEIGHT/2)+(HEIGHT/10),(int)((WIDTH/9)*1.5)/2,HEIGHT/140);

public G1P2()
{
    super("Radical Racing");
    setSize(WIDTH/9*10,HEIGHT/9*10);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setVisible(true);

    Move1  m1 = new Move1();
    Move2 m2 = new Move2();
    m1.start();
    m2.start();


}
Image offScreenImage  = null;


public void paint(Graphics g)
{
    super.paint(g);

    g.setColor(Color.DARK_GRAY);
    g.fillRect(0, 0, WIDTH, HEIGHT);

    g.setColor(Color.GREEN);


    g.fillRect(left.x, left.y, left.width, left.height);
    g.fillRect(right.x, right.y, right.width, right.height);
    g.fillRect(top.x, top.y, top.width, top.height);
    g.fillRect(bottom.x, bottom.y, bottom.width, bottom.height);
    g.fillRect(center.x, center.y, center.width, center.height);
    g.fillRect(obstacle.x, obstacle.y, obstacle.width, obstacle.height);
    g.fillRect(obstacle2.x, obstacle2.y, obstacle2.width, obstacle2.height);
    g.fillRect(obstacle3.x, obstacle3.y, obstacle3.width, obstacle3.height);
    g.fillRect(obstacle4.x, obstacle4.y, obstacle4.width, obstacle4.height);
    g.fillRect(obstacle5.x, obstacle5.y, obstacle5.width, obstacle5.height);

    g.setColor(Color.WHITE);
    g.fillRect(lineO.x, lineO.y, lineO.width, lineO.height);
    g.fillRect(lineI.x, lineI.y, lineI.width, lineI.height);

    g.setColor(Color.YELLOW);
    g.fillRect(finish.x, finish.y, finish.width, finish.height);

    g.setColor(Color.BLUE);
    g.fill3DRect(p1.x, p1.y, p1.width,p1.height,true);

    g.setColor(Color.RED);
    g.fill3DRect(p2.x, p2.y, p2.width, p2.height, true);
}

public void update(Graphics g)
{
    if(offScreenImage == null){
        offScreenImage = this.createImage(WIDTH, HEIGHT);
    }
    Graphics gOff = offScreenImage.getGraphics();
    paint(gOff);
    g.drawImage(offScreenImage, 0,0,null);
}

private class Move1 extends Thread
{
    public void run()
    {
        while(true)
        {
            try {
                repaint();
                if(p1Speed<=5)
                {
                    p1Speed +=0.2;
                }
                p1.y-=p1Speed;
                Thread.sleep(75);
            } catch (Exception e) {
                // TODO Auto-generated catch block
                break;
            }
        }
    }
}
private class Move2 extends Thread
{
    public void run()
    {
        while(true)
        {
            try {
                repaint();
                if(p2Speed<=5)
                {
                    p2Speed +=0.2;
                }
                p2.y-=p2Speed;
                Thread.sleep(75);
            } catch (Exception e) {
                // TODO Auto-generated catch block
                break;
            }
        }
    }
}
public static void main(String[] args) {
    new G1P2();
}

}

应该如何修改代码才能不闪烁！求指导。。。。