How to resize frame dynamically with Timer?

Question

I\'m trying to resize a window dynamically using a Timer object, but not succeeding... I set the preferred size of the panel in the constructor, which sets the size of the windo

Answer 1

You need to re-pack your JFrame to resize it. For instance at the end of your ActionListener:

Window win = SwingUtilities.getWindowAncestor(panel);
win.pack();

A question for you though: Why in heaven's name is your class extending JApplet and not JPanel? Or if it needs to be an applet, why are you stuffing it into a JFrame?

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Edit
Regarding your comment:

Wouldn't it usually be extending JFrame not JPanel? I'm stuffing it into a JFrame to allow it to run as an application as well as an applet. That's how 'Introduction to Java Programming' tells me how to do it :p Adding your code at the end of the actionPerformed method didn't do anything for me ;o

Most of your GUI code should be geared towards creating JPanels, not JFrames or JApplets. You can then place your JPanels where needed and desired without difficulty. Your book has serious issues and should not be trusted if it is telling you this.

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Edit 2
Works for me:

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

@SuppressWarnings("serial")
public class ShrinkingGui extends JPanel {
   private static final int INIT_W = 400;
   private static final int INIT_H = INIT_W;
   private static final int TIMER_DELAY = 20;
   private int prefW = INIT_W;
   private int prefH = INIT_H;

   public ShrinkingGui() {
      new Timer(TIMER_DELAY, new TimerListener()).start();;
   }

   public Dimension getPreferredSize() {
      return new Dimension(prefW, prefH);
   }

   private class TimerListener implements ActionListener {
      @Override
      public void actionPerformed(ActionEvent e) {
         if (prefW > 0 && prefH > 0) {
            prefW--;
            prefH--;
            Window win = SwingUtilities.getWindowAncestor(ShrinkingGui.this);
            win.pack();
         } else {
            ((Timer)e.getSource()).stop();
         }
      }
   }

   private static void createAndShowGUI() {
      ShrinkingGui paintEg = new ShrinkingGui();

      JFrame frame = new JFrame("Shrinking Gui");
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.getContentPane().add(paintEg);
      frame.pack();
      frame.setLocationRelativeTo(null);
      frame.setVisible(true);
   }

   public static void main(String[] args) {
      SwingUtilities.invokeLater(new Runnable() {
         public void run() {
            createAndShowGUI();
         }
      });
   }
}