双缓冲技术：

另一种减小帧之间的闪烁的方法是使用双缓冲,它在许多动画applet

中被使用。

主要原理是创建一个后台图象,将一帧画入图象,然后调用drawImage()

将整个图象一次画到屏幕上去。好处是大部分绘制是离屏的。将离屏图象一次

绘至屏幕上比直接在屏幕上绘制要有效得多。

双缓冲可以使动画平滑,但有一个缺点,要分配一张后台图象,如果图象

相当大,这将需要很大一块内存。

当你使用双缓冲技术时,应重载update()。

-Double-buffering technology:

　　　　　　　　Another reducing flicker between frames is to use double buffering, which in many animation applet

　　　　Was used.

　　　　　　　　The main principle is to create a background image, to a painting into the images, then call drawImage ()

　　　　The entire image to the screen a picture up. Advantage is that most of the drawing is off screen. An off-screen image will

　　　　Drawn to the screen than drawing directly on the screen to be much more effective.

　　　　　　　　Double buffering can make the animation smooth, but there is a drawback, to assign a background image, if image

　　　　Quite large, this will require a lot of memory.

　　　　　　　　When you use double buffering techniques should override update ().