我用Google搜索并找到了解决方案，是这样的:

I googled and i find the solution, and is this:

       WindowEvent closingEvent = new WindowEvent(frame, WindowEvent.WINDOW_CLOSING);
       Toolkit.getDefaultToolkit().getSystemEventQueue().postEvent(closingEvent);
       frame.setVisible(true);

它使用WindowEvent进行与"x"点击相同的操作.

It uses a WindowEvent to do the same as "x" click does.

无论如何，谢谢你们的帮助！

Thank you guys anyway for your help!!!