java用applet画图用到的方法(涉及双缓冲)

package bear.game.keyevent;
import java.applet.Applet;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.Rectangle;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
public class Game extends Applet implements KeyListener{
private Image bufImage = null;
Graphics bufG = null;
@Override
public void paint(Graphics g) {
setBackground(backColor);
g.fillRect(r.x, r.y, r.width, r.height);
}
@Override
public void update(Graphics g) {
bufImage = createImage(getSize().width, getSize().height);
bufG = bufImage.getGraphics();
paint(bufG);
g.drawImage(bufImage, 0, 0, null);
}
private static final long serialVersionUID = 1L;
private Rectangle r;
private Color backColor;
public void init()
{
r = new Rectangle(0, 0, 20, 10);
backColor = Color.WHITE;
addKeyListener(this);
}
@Override
public void keyPressed(KeyEvent e) {
int kc = e.getKeyCode();
if(kc == KeyEvent.VK_LEFT)
{
r.x -= 5;
if(r.x < 0)
r.x = 0;
repaint();
}
else if(kc == KeyEvent.VK_RIGHT)
{
r.x += 5;
if(r.x > getSize().width - r.width)
r.x = getSize().width - r.width;
repaint();
}
else if(kc == KeyEvent.VK_UP)
{
r.y -= 5;
if(r.y < 0)
r.y = 0;
repaint();
}
else if(kc == KeyEvent.VK_DOWN)
{
r.y += 5;
if(r.y > getSize().height - r.height)
r.y = getSize().height - r.height;
repaint();
}
}
@Override
public void keyReleased(KeyEvent e) {
// TODO Auto-generated method stub
}
@Override
public void keyTyped(KeyEvent e) {
// TODO Auto-generated method stub
char kc = e.getKeyChar();
switch(kc)
{
case 'r':
{
backColor = Color.RED;
repaint();
break;
}
case 'g':
{
backColor = Color.GREEN;
repaint();
break;
}
case 'b':
{
backColor = Color.BLUE;
repaint();
break;
}
case 'w':
{
backColor = Color.WHITE;
repaint();
break;
}
}
}
}

@Override
public void update(Graphics g) {
bufImage = createImage(getSize().width, getSize().height);
bufG = bufImage.getGraphics();
paint(bufG);
g.drawImage(bufImage, 0, 0, null);
}

/**
* Updates the container. This forwards the update to any lightweight
* components that are children of this container. If this method is
* reimplemented, super.update(g) should be called so that lightweight
* components are properly rendered. If a child component is entirely
* clipped by the current clipping setting in g, update() will not be
* forwarded to that child.
*
* @param g the specified Graphics window
* @see
Component#update(Graphics)
*/
public void update(Graphics g){
if(isShowing()) {
if(!(peer instanceof LightweightPeer)){
g.clearRect(0， 0， width， height);
}
paint(g);
}
}