说明： 编写程序，在Applet中生成一个蓝色的反弹球。该球用一个mousePressed事件初始化。当球碰到Applet边框时，它应该被弹起并沿反方向运动。 (preparation procedures, the applet generated a rebound in the blue ball. The ball incident with a mousePressed initialization. When the ball hits the rim Applet, it should be thrown up along the opposite direction and movement.)
