问如何在Java中仅当我的框架在屏幕上消失时进行操作？

EN

import java.awt.event.WindowEvent;
import java.awt.event.WindowListener;
import javax.swing.JFrame;
import javax.swing.JLabel;

public class MainFrame extends JFrame implements WindowListener {

    public MainFrame() {

        super("Test Frame");
        JLabel displayMsg = new JLabel("    Close window");
        getContentPane().add(displayMsg);

        addWindowListener(this);
        setSize(400, 300);
        setVisible(true);

    }

    @Override
    public void windowClosing(WindowEvent e) {

        System.out.println("WindowListener method called: windowClosing.");
        //add you screen capture code here
    }

  //--Not used

    @Override
    public void windowClosed(WindowEvent e) {
        //do nothing
    }

    @Override
    public void windowOpened(WindowEvent e) {
       //do nothing
    }

    @Override
    public void windowIconified(WindowEvent e) {
         //do nothing
    }

    @Override
    public void windowDeiconified(WindowEvent e) {
         //do nothing
    }

    @Override
    public void windowActivated(WindowEvent e) {
         //do nothing
    }

    @Override
    public void windowDeactivated(WindowEvent e) {
         //do nothing
    }

    public void windowGainedFocus(WindowEvent e) {
         //do nothing
    }

    public void windowLostFocus(WindowEvent e) {
         //do nothing
    }

    public static void main(String[] args) {
         new MainFrame();
    }
}

  useRobotToMakeScreenshot();

  javax.swing.SwingUtilities.invokeLater(new Runnable() {
      public void run() {
          useRobotToMakeScreenshot();
      }
  }