public void update(Graphics g){
BufferedImage ImageBuffer = new BufferedImage(450,300,1);
Graphics GraImage = ImageBuffer.getGraphics();//获取图形缓冲区的图形上下文
// GraImage.dispose();//////////这要写到后面
GraImage.fillRect(120,120,150,30);
g.drawImage(ImageBuffer, 0, 0, this);//将图形缓冲区绘制到屏幕上
}