Window screen flicker problem

Write a snow program , but the interface is blinking , who can help me correct it, very grateful !

import java.awt.*; 
  import java.awt.event.*;
  import javax.swing.*;
  class Table extends Frame implements ActionListener
  {
  	Button start=new Button("开始");
  	int[] xx = new int [100];
      int[] yy = new int [100];
      int[]fs1 = new int [100];  
      Font fs = null;
  	public Table()
  	{
  		super("雪花飞");
  		setSize(1200,800); 
  		setBackground(Color.black); 
  		//setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  		setVisible(true);
  		setLayout(new FlowLayout());
  		add(start);
  		start.addActionListener(this);
  		validate();
  		addWindowListener(new WindowAdapter()
  		{
  		 public void windowClosing (WindowEvent e){System.exit(0);}
  		});
  	}
  
   public void actionPerformed(ActionEvent e)
    {
  	if(e.getSource()==start)begin();
    }
    public void begin()
  	{ 
  	 for(int i=0;i<xx.length;i++)
  		{  
  		  xx[i]=(int)(1200*Math.random());
  		  yy[i]=(int)(800*Math.random());
  		  fs1[i]=(int)(20*Math.random()+12);  
  	   }		  		
  	new Thread(){
  	 public void run()
  		{
  		 while(true)
  			 {
  			 for(int i=0;i<xx.length;i++)
  					{  	  
  						 if((yy[i]>800)||(yy[i]<0))yy[i] =0;
  						 yy[i]++; 
  					 }
  					 repaint();
  					try{ Thread.sleep(10);} catch(InterruptedException e)
  						{System.err.println("Thread interrupted");}
  			}
  		 }
  				}.start();
  	}
  	public void paint(Graphics g)
  		{	
  		  super.paint(g);
  		  Image img=new ImageIcon("11.jpg" ).getImage();
  		  g.drawImage(img,0,0,1200,800,null);
     		  for(int i=0;i<xx.length;i++)
  			{  
  			Font fs =new Font("宋体",Font.BOLD,fs1[i]);     
  			g.setColor(Color.white);
  			g.setFont(fs);
  			g.drawString("*",xx[i],yy[i]);//画雪花
  			}
  		}
  	public static void main(String args[])
  	{
  		new Table();
  	}
  }

------ Solution ------------------------------------- -------

  import java.awt.*;
  import java.awt.event.*;
  import javax.swing.*;
  
  public class Table extends Frame implements ActionListener {
  	Button start = new Button("开始");
  	int[] xx = new int[100];
  	int[] yy = new int[100];
  	int[] fs1 = new int[100];
  	Font fs = null;
  	Image offScreen = null;
  	
  	public Table() {
  		super("雪花飞");
  		setSize(1200, 800);
  		//setBackground(Color.black);
  		// setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  		setVisible(true);
  		setLayout(new FlowLayout());
  		add(start);
  		start.addActionListener(this);
  		validate();
  		addWindowListener(new WindowAdapter() {
  			public void windowClosing(WindowEvent e) {
  				System.exit(0);
  			}
  		});
  	}
  
  	public void actionPerformed(ActionEvent e) {
  		if (e.getSource() == start)
  			begin();
  	}
  
  	public void begin() {
  		for (int i = 0; i < xx.length; i++) {
  			xx[i] = (int) (1200 * Math.random());
  			yy[i] = (int) (800 * Math.random());
  			fs1[i] = (int) (20 * Math.random() + 12);
  		}
  		new Thread() {
  			public void run() {
  				while (true) {
  					
  					repaint();
  					try {
  						Thread.sleep(10);
  					} catch (InterruptedException e) {
  						System.err.println("Thread interrupted");
  					}
  				}
  			}
  		}.start();
  	}
  
  	public void paint(Graphics g) {
  		super.paint(g);
  		g.setColor(Color.BLACK);
  		g.fillRect(0, 0, 1200, 800);
  		//Image img = new ImageIcon("11.jpg").getImage();
  		//g.drawImage(img, 0, 0, 1200, 800, null);
  		for (int i = 0; i < xx.length; i++) {
  			Font fs = new Font("宋体", Font.BOLD, fs1[i]);
  			g.setColor(Color.white);
  			g.setFont(fs);
  			g.drawString("*", xx[i], yy[i]);// 画雪花
  		}
  		
  		for (int i = 0; i < xx.length; i++) {
  			if ((yy[i] > 800) || (yy[i] < 0))
  				yy[i] = 0;
  			yy[i]++;
  		}
  	}
  
  	public void update(Graphics g) {
  		if(offScreen == null) {
  			offScreen = createImage(1200, 800);
  		}
  		Graphics gOffScreen = offScreen.getGraphics();
  		paint(gOffScreen);
  		g.drawImage(offScreen, 0, 0, null);
  	}
  	
  	public static void main(String args[]) {
  		new Table();
  	}
  }

I'll give you a picture annotated
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double buffering , rewritten update function
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er er, online search, but the method is not overridden , the method gives better downstairs ! Thanks!
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er er, thank you, online search is rewritten, but did not give way to speak with you this fact ! Thank you !
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  said summed up , novice or not ah
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       said summed up , novice or not ah     

I am also a novice, if you do not , you can look Refbacks tanks picture version of the video , which will have a specific update function to rewrite , you want to see , then you can download http://pan.baidu.com/ share / link? shareid = 379477633 & uk = 202436276
reasons:
1. refresh frequency too fast redraw , paint method is not yet complete
2. displayed one by one
solution: all the things painted on the virtual image , disposable displayed

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offScreen has been declared over, first determine whether it is empty , then there is no longer initialized