请教java小程序的一点问题

Question

修改一下scroll():    void scroll() {
        while (true)
        {
            y = y - 1;
            if (y < -75)
            {
                y = 76;
            }
                repaint();
                try
                {
                 Thread.sleep(250);
                }
                catch (InterruptedException e) {
                 e.printStackTrace();
                }
        }
    }