thirdwindow.java

《A first book of java》by Gary J.Bronson 北大出版社

import javax.swing.*;
import java.awt.event.*;  // this is needed for the event handlers
public class ThirdWindow extends JFrame
{
  private JFrame mainFrame;

  public ThirdWindow() // a constructor
  {
    mainFrame = new JFrame("Third GUI Window");

   
    mainFrame.setSize(300,150);
    mainFrame.show();

    WinHandler handler = new WinHandler();  // Step 2 - create an event handler
    mainFrame.addWindowListener(handler);  // Step 3 - register (activate) the handler
  } 
    
  public static void main(String args[])
  {
    new ThirdWindow(); 
  }
}  // end of GUI class

  // Step 1 - define a listener class to handle window events
class WinHandler implements WindowListener
{
  public void windowClosing(WindowEvent e) {System.exit(0);}
  public void windowClosed(WindowEvent e) {}
  public void windowOpened(WindowEvent e) {}
  public void windowIconified(WindowEvent e) {}
  public void windowDeiconified(WindowEvent e) {}
  public void windowActivated(WindowEvent e) {}
  public void windowDeactivated(WindowEvent e) {}
}  // end of listener class