java双缓冲无法显示图片

[ttfjya]

import java.awt.event.*;
import java.awt.*;
import java.applet.*;

public class MyPuzzles extends Applet {
	/**
	* 
	*/
	private static final long serialVersionUID = 1L;
	private Image []pic;
	private boolean able;
	private int lasty;
	private int lastx;
	private Font font;
	final int WIDTH = 480;
	final int HEIGHT = 600;
	private Image off_screen;
	private Graphics off_buffer;
	
	public void init() {
		
		resize(600,600);
		setBackground(Color.orange);
		pic = new Image[3];
		font = new Font("TimesRoman", Font.BOLD, 48);
		pic[0] = getImage(getCodeBase(), "im1.jpg");
		pic[1] = getImage(getCodeBase(), "img2.jpg");
		pic[2] = getImage(getCodeBase(), "img3.jpg");
		MediaTracker media = new MediaTracker(this);
		media.addImage(pic[0], 0);
		media.addImage(pic[1], 0);
		media.addImage(pic[2], 0);
		try {
			media.waitForID(0);
		} catch (InterruptedException e) {
			System.out.println("fail to load the pictures");
		}

}
	public void paint(Graphics g) {
		if(off_screen == null){
			off_screen = creatImage(WIDTH, HEIGHT);
			off_buffer = off_screen.getGraphics();
		}
			off_buffer.setColor(Color.black);
			off_buffer.fillRect(0, 0, WIDTH, HEIGHT);
			off_buffer.drawImage(pic[0], 50, 35, 160,250, this);
			off_buffer.drawImage(pic[1], 70, 300, 160,250, this);
			off_buffer.drawImage(pic[2], 300, 200, 160,250, this);
			off_buffer.setColor(Color.red);
			off_buffer.setFont(font);
			off_buffer.drawString("Choose one!", 240, 90);
		g.drawImage(off_screen, 0, 0, this);
	}
	
   }

}
不能把off_buffer中的图片显示出来。。。。