能不能请各位帮小弟看一下，为什么我用了双缓冲技术后仍然闪屏现象严重？

[it小小白痴]

package com.Test;

import javax.swing.JApplet;
import javax.swing.JButton;

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.event.ActionListener;
import java.util.Vector;
import java.awt.event.ActionEvent;

class Ball
{
    final int max_speed = 5;  //小球最大速度
    final int radius = 30;  //小球半径
    final int height = 380, width = 450;  //运动区域的高度和宽度
    int x = (int)(Math.random() * (width - radius));     //初始横坐标
    int y = (int)(Math.random() * (height - radius));    //初始纵坐标
    int dx = (int)(Math.random() * max_speed), dy = (int)(Math.random() * max_speed);   //坐标改变值
    
    public void run()
    {
        if (width - radius - x - dx < 0 || x + dx - radius < 0)  //判断越界
        {
            dx = -dx;
        }
        if (height - radius - y - dy < 0 || y + dy - radius < 0)
        {
            dy = -dy;
        }
        
        //运动过程
        x += dx;
        y += dy;
    }
}

public class Collision_Ball extends JApplet implements Runnable
{
    final int height = 450, width = 450;  //界面大小
    Vector<Ball> balls = new Vector<Ball>();  //所有小球

    //常用颜色集合
    Color[] popular = {Color.BLACK, Color.BLUE, Color.CYAN, Color.GRAY, Color.GREEN, Color.MAGENTA, Color.ORANGE,
        Color.PINK, Color.RED, Color.YELLOW};
    Image offScreen = null;
    
    public void paint(Graphics g)
    {
        super.paint(g); // 轻量级组件不调用update
        for (int i = 0; i < balls.size(); i++)
        {
            g.setColor(popular[i % popular.length]);  //按顺序取一个颜色
            g.fillOval(balls.elementAt(i).x,
                balls.elementAt(i).y,
                balls.elementAt(i).radius,
                balls.elementAt(i).radius);
            balls.elementAt(i).run();
            // ball.print=true;
        }
    }
    
    public void update(Graphics g)  //双缓冲技术
    {
        if (offScreen == null)
        {
            offScreen = createImage(width, height);
        }
        Graphics gOffScreen = offScreen.getGraphics();
        paint(gOffScreen);
        g.drawImage(offScreen, 0, 0, null);
    }
    
    public Collision_Ball()
    {
        init();
    }
    
    Thread my_applet = null;
    
    public void init()
    {
        getContentPane().setLayout(null);
        getContentPane().setBounds(0, 0, width, height);
        JButton button = new JButton("\u6DFB\u52A0\u5C0F\u7403");
        button.addActionListener(new ActionListener()
        {
            public void actionPerformed(ActionEvent e)
            {
                balls.addElement(new Ball());  //按下按钮就增加一个新球
                repaint();
                // balls.elementAt(balls.size()-1).start();
            }
        });
        final int x = 0, y = 380;
        button.setBounds(x, y, width - x, height - y);
        button.setFont(new Font("微软雅黑", Font.PLAIN, 20));
        getContentPane().add(button);
        
        my_applet = new Thread(this);
        my_applet.start();
    }
    
    @Override
    public void run()
    {
        while (true)
        {
            if (!balls.isEmpty())  //如果还有小球就开始运动
            {
                repaint();
                try
                {
                    Thread.sleep(5);
                }
                catch (InterruptedException e)
                {
                    // TODO 自动生成的 catch 块
                    e.printStackTrace();
                }
            }
        }
    }
    
    public void start()
    {
        
    }
    
    public void stop()
    {
        balls.clear();
    }
}