请问一下为什么这个APPLET总是闪烁？？谢谢

[RabbitLBJ]

是一个转盘程序，在转的时候总是要闪烁。。
先上代码，解释在后面，谢谢！！

import java.applet.*;
import java.awt.*;
import java.util.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.geom.Rectangle2D;
import java.awt.image.BufferedImage;
import java.awt.image.CropImageFilter;
import java.awt.image.FilteredImageSource;
import java.awt.image.ImageProducer;


public class test extends Applet implements Runnable,ActionListener{
	
	private Image img;
	private Image[] arr;
	private Image background;
	private Image offscreen;
	private BufferedImage bi;
	private MediaTracker mt;
	private Thread animation;

	
	private int y;
	private int iWheela,iWheelb,iWheelc;
	private int iCounta,iCountb,iCountc;
	private boolean bStopa,bStopb,bStopc;
	private int iResulta,iResultb,iResultc;
	private boolean bFirst;
	private Random rand;

	
	private Panel panel;
	private Button button,up,down;
	private TextField t1,t2;
	private int score,debt;
	
	public void init()
	{
		setSize(600,300);
		iWheela=iWheelb=iWheelc=0;
		iCounta=iCountb=iCountc=7;
		bStopa=bStopb=bStopc=false;
		bFirst=true;
		score=20;
		debt=0;
		rand=new Random();
		bi=new BufferedImage(75,105,BufferedImage.TYPE_INT_RGB);
	
		mt=new MediaTracker(this);
		arr=new Image[30];
		img=getImage(getCodeBase(),"wheel.gif");
		mt.addImage(img, 0);
		try{
			mt.waitForID(0);
		}catch(InterruptedException e){}

		background=getImage(getCodeBase(),"background.jpg");
		mt.addImage(background, 0);
		try{
			mt.waitForID(0);
		}catch(InterruptedException e){}
		
		
		offscreen=this.getGraphicsConfiguration().createCompatibleVolatileImage(getSize().width, getSize().height);
		
		for(int i=0;i<30;i++)
		{
			arr[i]=createImage(new FilteredImageSource(img.getSource(),new CropImageFilter(0,y,100,100)));
			y+=20;
			mt.addImage(arr[i], 0);
			try{
				mt.waitForAll();
			}catch(InterruptedException e){}
		}
		
		setLayout(new BorderLayout());
		panel=new Panel();
		panel.setLayout(new GridLayout(5,1));
		button=new Button("开始");
		t1=new TextField(""+score,20);
		t2=new TextField(""+debt,20);
		up=new Button("增加");
		down=new Button("减少");
		panel.add(button);
		panel.add(t1);
		panel.add(t2);
		panel.add(up);
		panel.add(down);
		button.addActionListener(this);
		up.addActionListener(this);
		down.addActionListener(this);
		add(panel,BorderLayout.EAST);

		y=0;
	
		
	}
	
	public void start()
	{
		if(animation==null)
		{
			iWheela=iWheelb=iWheelc=0;
			iCounta=iCountb=iCountc=7;
			bStopa=bStopb=bStopc=false;
			animation=new Thread(this);
		}
		if(bFirst)
		{
			bFirst=false;
			animation=null;
			return;
		}
			
		animation.start();
	
	}
	
	
	public void stop()
	{
		
		animation=null;

	}
	
	public void run()
	{
		
		Thread cur=Thread.currentThread();	
		while(cur==animation)
		{
			try{
				Thread.sleep(20);
				
			}catch(InterruptedException e){
				break;
			}
			if(!bStopa)
				iWheela++;
			if(!bStopb)
				iWheelb++;
			if(!bStopc)
				iWheelc++;
			if(bStopa && bStopb && bStopc)
			{
				calculate();
				stop();
			}
			update();	
		}
		
	
	}
	
	public void paint(Graphics g)
	{
		Graphics2D g2d=(Graphics2D)offscreen.getGraphics();
		
		g2d.drawImage(background,0,0,this);
		((Graphics2D)bi.getGraphics()).drawImage(arr[iWheela%30],0,0,bi.getWidth(this),bi.getHeight(this),this);
		g2d.drawImage(bi, null, 50, 90);
		((Graphics2D)bi.getGraphics()).drawImage(arr[iWheelb%30],0,0,bi.getWidth(this),bi.getHeight(this),this);
		g2d.drawImage(bi, null, 140, 90);
		((Graphics2D)bi.getGraphics()).drawImage(arr[iWheelc%30],0,0,bi.getWidth(this),bi.getHeight(this),this);
		g2d.drawImage(bi, null, 230, 90);

		g2d.dispose();
		
		g.drawImage(offscreen,0,0,this);	
	}
	
	public void update()
	{
		if(!bStopa)
		{
			if((iWheela%5)==0)
			{
				if(rand.nextBoolean())
				{
					iCounta--;
					if(iCounta==0)
					{
						iResulta=iWheela%30;
						bStopa=true;
					}
						
				}
			}
		}
			
		if(!bStopb)
		{
			if((iWheelb%5)==0)
			{
				if(rand.nextBoolean())
				{
					iCountb--;
					if(iCountb==0)
					{
						iResultb=iWheelb%30;
						bStopb=true;
					}
				}
			}
		}
		
		if(!bStopc)
		{
			if((iWheelc%5)==0)
			{
				if(rand.nextBoolean())
				{
					iCountc--;
					if(iCountc==0)
					{
						iResultc=iWheelc%30;
						bStopc=true;
					}
				}
			}
		}
		
		
		if(offscreen==null || offscreen.getWidth(null)!=getSize().width ||
		   offscreen.getHeight(null)!=getSize().height)
		{
			offscreen=createImage(getSize().width,getSize().height);
		}
		repaint();
	}
	
	public void actionPerformed(ActionEvent e)
	{
		if(e.getSource()==button)
		{
			start();
		}
		if(e.getSource()==up)
		{
			if(score>0 && debt<10)
			{
				score--;
				debt++;
				t1.setText(""+score);
				t2.setText(""+debt);
			}
		}
		if(e.getSource()==down)
		{
			if(debt>0)
			{
				score++;
				debt--;
				t1.setText(""+score);
				t2.setText(""+debt);
			}
				
		}
	}
	
	public void calculate()
	{
		if(iResulta==iResultb && iResulta==iResultc)
		{
			score+=debt*3;
			debt=0;
			t1.setText(""+score);
			t2.setText(""+debt);
			
		}
		else if(iResulta==iResultb || iResulta==iResultc || iResultb==iResultc)
		{
			score+=debt*2;
			debt=0;
			t1.setText(""+score);
			t2.setText(""+debt);
		}
		else
		{
			debt=0;
			t1.setText(""+score);
			t2.setText(""+debt);
		}
		
	}
	
}

看过图形编程的书，说要避免闪烁可以使用后背缓冲，可是在这个APPLET里面我使用了啊，就是那个offscreen的IMAGE，都是先在他上面画图，然后一次性画在窗口里面的。请哪位高人帮忙解决一下，谢谢了

[RabbitLBJ]

帮帮忙，谢谢了！！急用啊

[lodachi]

看上去挺复杂 才给20分

[RabbitLBJ]

大哥，我只有20分了，干了都。。。
帮帮忙，谢谢