Multiple Windows in Java

Here is a small program that will create multiple windows (JFrame's), keep track of how many have been created, and exit the program when the last one is closed.

The code:

• Listens for event from a JButton to create instance of the class.
• Listens for window events in general,
  
• (yellow code) but uses the WindowAdapter class to only react to the window closing event.
• Exits the program when all the windows have been closed.
• Staggers the locations of the windows as they are created.
  

Code:

import javax.swing.JFrame;
import javax.swing.JButton;
import java.awt.BorderLayout;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;

public class ManyWindowsDemoND extends JFrame {
  public static final long serialVersionUID = 3; // ND: junk
  static int windowCount = 0;
  static int lastX = 20, lastY = 20, newWindowDelta = 40;
  
  public ManyWindowsDemoND () {
      windowCount ++;
      setTitle ("ManyWindowsDemoND: " + windowCount);
      setSize (400, 400);
     
      setLocation (lastX += newWindowDelta, lastY += newWindowDelta);

      addWindowListener (
         new WindowAdapter () {
            public void windowClosing (WindowEvent e) {
               windowCount --;
               if (windowCount == 0) System.exit (0);
            } // end closing event handler method
         } // end new inner adapter
      ); // end adding method
     
      JButton jbNewWindow = new JButton ("New JFrame");
      jbNewWindow.addActionListener (e -> new ManyWindowsDemoND ());
      add (jbNewWindow, BorderLayout.NORTH);

      setVisible (true);
      validate ();
  } // end no parameter constructor
 
  public static void main (String args []) {
    new ManyWindowsDemoND ();
  } // end method main
} // end class ManyWindowsDemoND

FrameND Notes

• This class creates cascading JFrames with reasonable default values
• FrameND will track how many frames have been instantiated
• and the program will only quit when the last frame is closed.
• There are 3 constructors:
• no parameter - various default values
• String parameter - used to set the title of the frame to something other than the default
• String-int-int parameters - used to set the title and the width and height of the frame.
• main method shows one way to use this program

FrameND Code

public class FrameND extends javax.swing.JFrame {
   public static final long serialVersionUID = 892374; // ND: junk
   static final int WIDTH = 400, HEIGHT = 200;
   static final int DX = 20, DY = 20;
  
   static int windowCount = 0;
   static FrameND prev = null;
  
   public FrameND () {
      windowCount ++;
      setSize (WIDTH, HEIGHT);
      if (windowCount == 1) {
         setLocationRelativeTo (null);
      }
      else {
         java.awt.Point p = prev.getLocation();
         setLocation (p.x + DX, p.y + DY);
      } // end creating cascading frames
      prev = this;
      validate ();
      setTitle ("Frame Number:  " + windowCount);
      setVisible (true);
   //     setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE);
      addWindowListener (
         new java.awt.event.WindowAdapter () {
            public void windowClosing (java.awt.event.WindowEvent e) {
               windowCount --;
               if (windowCount == 0) System.exit (0);
            } // end closing event handler method
         } // end new inner adapter
      ); // end adding anonymous inner class listener
   } // end no-parameter constructor
  
   public FrameND (String s) {
      this ();
      setTitle (s);
   } // String constructor
  
   public FrameND (String s, int w, int h) {
      this (s);
      setSize (w, h);
   } // end String-int-int constructor
  
   public static void main (String args []) {
      new FrameND ();
      new FrameND ();
      new FrameND ("Setting Size as well", 500, 100);
      new FrameND ("Another Frame");
      new FrameND ();
      System.out.println ("-- bye __");
   } // end main
} // end class FrameND