J2ME中使用缓存将屏幕内容存储为Image

class SimpleCanvas extends Canvas{ 
　int w; 
　int h; 
　private Image offImage = null; 
　private boolean buffered = true; 
　public SimpleCanvas(boolean _buffered){ 
　　buffered = _buffered; 
　　w = getWidth(); 
　　h = getHeight(); 
　　if(buffered) 
　　offImage = Image.createImage(w,h); 
　} 
　protected void paint(Graphics g) { 
　　int color = g.getColor(); 
　　g.setColor(0xFFFFFF); 
　　g.fillRect(0,0,w,h); 
　　g.setColor(color); 
　　Graphics save = g; 
　　if(offImage != null) 
　　　g = offImage.getGraphics(); 
　　　//draw the offimage 
　　　g.setColor(128,128,0); 
　　　g.fillRoundRect((w-100)/2,(h-60)/2,100,60,5,3); 
　　　//draw the offimage to the canvas 
　　　save.drawImage(offImage,0,0,Graphics.TOP|Graphics.LEFT); 
　} 
　public Image printMe(){ 
　　return offImage; 
　}

package com.J2MEdev; 
import Javax.microedition.midlet.*; 
import javax.microedition.lcdui.*; 
/** 
* 
* @author mingjava 
* @version 
*/ 
public class PrintScreen extends MIDlet implements CommandListener{ 
　private Display display = null; 
　private SimpleCanvas canvas = new SimpleCanvas(true); 
　private Command printCommand = new Command("Print",Command.OK,1); 
　public void startApp() { 
　　if(display == null) 
　　　display = Display.getDisplay(this); 
　　canvas.addCommand(printCommand); 
　　canvas.setCommandListener(this); 
　　display.setCurrent(canvas); 
　} 
　public void pauseApp() {} 
　public void destroyApp(boolean unconditional) {} 
　public void commandAction(Command command, Displayable displayable) { 
　　if(command == printCommand){ 
　　　Form form = new Form("screen"); 
　　　form.append(canvas.printMe()); 
　　　display.setCurrent(form); 
　　} 
　} 
}