java - 让球返回小程序

Question

这段代码只让球前进，如何让球返回？

我可以将它添加到循环中以使球返回到左侧的表达式是什么。

Applet Viewer

    public class NewJApplet extends JApplet {    
        public void paint(Graphics g) 
        {
            final int X=0;
            final int Y=50;
            final int DIAMETER=15;
            final Color COLOR= Color.BLACK;
            final int SPACE =5;
            // instantiate the ball as a Circle object
            Circle baall = new Circle(X,Y,DIAMETER,COLOR); 

 // get ball diameter and width & height of the applet window
            int ballDiam = baall.getDiameter();
            int windWidth= getWidth();
            int windHeight=getHeight();

// rolling horizontally
    // check whether ball is at right edge of window   
            while(baall.getX()+ballDiam<windWidth)
            {
                baall.draw(g);

                try {
                        Thread.sleep(50);
                    } catch (Exception e) {
                        System.out.println("There is an error in sleep ! ");
                }
// clear the window
                g.clearRect(0, 0, windWidth, windHeight);
// position to next location for drawing ball
                baall.setX(baall.getX()+SPACE);

            }
            baall.draw(g); // draw the ball in the current position
        }
    }

Answer 1

当球在窗口的右边缘时，我想你想把它带到 0,50。只需执行与将其带到右边缘的步骤相反的操作。

• 将 X 坐标设置为右边缘(尽量不要将 X、Y、DIAMETER、COLOR 作为最终坐标)并重新实例化 Circle 对象 baall

X = getWidth()-15;
baall=new Circle(X,Y,DIAMETER,COLOR);

• 检查球是否在左边缘 并绘制它。

while(baall.getX()-ballDiam>0) { 
    baall.draw(g); 
    try { 
        Thread.sleep(50); }
    catch(Exception e){ 
        System.out.println("There is an error in sleep ! "); 
    }

• 清除窗口并定位下一个位置

g.clearRect(0, 0, windWidth, windHeight);
baall.setX(baall.getX()-SPACE);
} //while

我想这会工作得很好:)