java - 如何使图像水平反弹？

Question

我有一个水平移动的图像(“ball.gif”)，问题是当球到达面板尺寸的末端时如何让球反弹？我知道这并不难，但我只是对如何去做有点困惑。

有人可以帮我解决这个问题吗？

这是我迄今为止尝试过的:

public void paint(Graphics g)
{
    super.paint(g);
    Graphics2D g2d = (Graphics2D)g;
   g2d.drawImage(ball, x, y, this);
   Toolkit.getDefaultToolkit().sync();

    g.dispose();
}


public void cycle()
{



    x += 1;
    y += 0;
    if (x >240)
    {


        x = 10;
        y = 10;
    }


}


public void run()
{

    long beforeTime, elapsedTimeDiff, sleep;

    beforeTime = System.currentTimeMillis();

    while (true)
    {

        cycle();
        repaint();

        elapsedTimeDiff = System.currentTimeMillis() - beforeTime;
        sleep = DELAY - elapsedTimeDiff;
        System.out.println(sleep);

        if (sleep < 0)
        {
            sleep = 2;
        }
        try
        {
            Thread.sleep(sleep);
        }
        catch (InterruptedException e)
        {
            System.out.println("interrupted");
        }

        beforeTime = System.currentTimeMillis();
    }
}

Answer 1

首先，您需要将速度保持在一个字段中，而不是对其进行硬编码:

private static final int RIGHT_WALL = 240;
private int x, y;
private int xVelocity = 1;


//...
x += xVelocity;
y += 0;  //change this later!

然后当你做边界检查时，翻转你的 xVelocity :

//...
if ( x > RIGHT_WALL ) {
   x = RIGHT_WALL;
   xVelocity *= -1;
}