Thread.sleep（）在预期时不会触发

Question

我想知道为什么Thread.sleep()没有在预期的时间点出现。

我期望绘制第一个矩形，暂停2秒，然后是第二个矩形的外观。 然而，暂停首先开始，然后两个矩形被“一次”绘制。

为什么会出现这种情况？

提前感谢任何建议。

public class Figure extends JPanel

{

  Point a = new Point(10, 10);

  Point b = new Point(110, 10);

  Point c = new Point(110, 110);

  Point d = new Point(10, 110);

  @Override
  protected void paintComponent(Graphics g)
  {

    super.paintComponent(g);

    g.drawLine(a.x, a.y, b.x, b.y);

    g.drawLine(b.x, b.y, c.x, c.y);

    g.drawLine(c.x, c.y, d.x, d.y);

    g.drawLine(d.x, d.y, a.x, a.y);

    try
    {
      Thread.sleep(2000);
    }
    catch(InterruptedException ex)
    {
    }
    Point newA = rotate(a, 45);
    Point newB = rotate(b, 45);
    Point newC = rotate(c, 45);
    Point newD = rotate(d, 45);

    g.drawLine(newA.x, newA.y, newB.x, newB.y);
    g.drawLine(newB.x, newB.y, newC.x, newC.y);
    g.drawLine(newC.x, newC.y, newD.x, newD.y);
    g.drawLine(newD.x, newD.y, newA.x, newA.y);
  }

  private Point rotate(Point p, int degree)

  {

    //to shift the resulting Point some levels lower
    int offset = 100;

    int x = (int)(Math.cos(degree) * p.x + Math.sin(degree) * p.y);
    int y = (int)(-Math.sin(degree) * p.x + Math.cos(degree) * p.y) + offset;

    Point ret = new Point(x, y);
    return ret;
  }

}

Answer 1

这是因为您没有进入Swings事件循环; 只有这样才能保证执行paint命令。 此外，这也是为什么永远不要在事件循环线程中睡觉的一个原因...

Answer 2

我将第二个矩形的代码更改为

try
{
  Thread.sleep(2000);
}

catch(InterruptedException ex)
{
}

a = rotate(a, 45);
b = rotate(b, 45);
c = rotate(c, 45);
d = rotate(d, 45);

g.drawLine(a.x, a.y, b.x, b.y);
g.drawLine(b.x, b.y, c.x, c.y);
g.drawLine(c.x, c.y, d.x, d.y);
g.drawLine(d.x, d.y, a.x, a.y);

方法paintComponent似乎是通过pereptually运行的：现在一个矩形旋转，它的前身消失等等......

Answer 3

调用所有这些绘制方法并没有物理绘制任何东西，它只是将绘图命令放入图形管道中，而你所有的sleep（）正在做的是阻止管道的处理。 你应该做的是切换一个变量，该变量告诉方法绘制哪些位，并以所需的间隔从一个单独的线程向外部触发repaint（）。

Answer 4

永远不要在AWT事件线程中使用Thread.sleep（）（例如paintComponent（）或各种onclick处理程序，它们总是在AWT事件线程中运行） - 阻止所有事件被处理 - 键，鼠标等，你的应用程序将看起来像是冻结了。 一个快速而肮脏的解决方案：

private boolean isRotating = false;

 @Override
protected void paintComponent(Graphics g)
{
  super.paintComponent(g);
  if (!isRotating) {
  g.drawLine(a.x, a.y, b.x, b.y);
  g.drawLine(b.x, b.y, c.x, c.y);
  g.drawLine(c.x, c.y, d.x, d.y);
  g.drawLine(d.x, d.y, a.x, a.y);
  isRotating = true;
  Utils.swingInvokeDelayed(new Runnable() { public void run(){ repaint();}}, 2000);
} else {
  Point newA = rotate(a, 45);
  Point newB = rotate(b, 45);
  Point newC = rotate(c, 45);
  Point newD = rotate(d, 45);
  g.drawLine(newA.x, newA.y, newB.x, newB.y);
  g.drawLine(newB.x, newB.y, newC.x, newC.y);
  g.drawLine(newC.x, newC.y, newD.x, newD.y);
  g.drawLine(newD.x, newD.y, newA.x, newA.y);
  isRotating = false;
}
}

public class Utils {
// ideal is to keep 0 as corePoolSize, but then the executor simply does not work :(
private static final ScheduledExecutorService executor = Executors.newScheduledThreadPool(1, newDaemonThreadFactory(Utils.class.getSimpleName()));
private static ThreadFactory newDaemonThreadFactory(final String threadName) {
    return new ThreadFactory() {

        public Thread newThread(Runnable r) {
            final Thread result = new Thread(r, threadName);
            result.setDaemon(true);
            return result;
        }
    };
}
public static void swingInvokeDelayed(final Runnable r, final long delay) {
    executor.schedule(new Runnable() {

        public void run() {
            SwingUtilities.invokeLater(r);
        }
    }, delay, TimeUnit.MILLISECONDS);
}
}

Answer 5

Swingworker就是你要找的