I am getting some odd behaviour with respect to the five-parameter version
of JOptionPane.showMessageDialog() in J2SE 1.5 on Windows XP: the icon I am
specifying does not appear in my JOptionPane.

I know that the icon is being found and loaded correctly; the icon is
definitely present and  not null in the debugger just before I invoke
showMessageDialog() so this *appears* to be a bug in showMessageDialog().
However, this method is pretty mature code and has been around since the
early days of Swing so I'm inclined to doubt that the code is buggy or it
would have been spotted long before now. I just checked the Bug Database and
couldn't find any other reports of this problem. That reinforces my
suspicion that it is not a bug in showMessageDialog(): this method must be
very widely used so if there was a bug in the method, surely hundreds of
people would have seen it by now.

That leads me to think I've done something wrong in my code, although I
certainly can't see a mistake. I was hoping someone here could try this code
and either:
a) verify that they are seeing this problem and it really is a bug -OR-
b) tell me what I've done wrong

If it is a real bug, I'll report it to the Bug Database.

To run my code and see the problem, all you need to do is supply the name of
a valid GIF, JPG, or PNG file in the argument of the 'getResource()' method
on the line that starts 'URL aboutIconUrl ='.

The three buttons illustrate different versions of showMessageDialog():
- 'About 1' uses the four-argument version of showMessageDialog(), the one
that uses the default icon, and works perfectly.
- 'About 2' uses the five-argument version of showMessageDialog() but has
the icon set to null; it simply displays the default icon and therefore has
the same result as 'About 1', which I assume is the correct result.
- 'About 3' demonstrates the problem because a valid non-default icon is
passed to the five-argument version of showMessageDialog() yet no icon, even
the default icon, is displayed in the dialog.

--TempAbout.java--------------------------------

import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.UnsupportedEncodingException;
import java.net.URL;
import java.net.URLDecoder;

import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JOptionPane;

public class TempAbout extends JFrame implements ActionListener {

   public static void main(String[] args) {

       TempAbout tempAbout = new TempAbout();
       tempAbout.pack();
       tempAbout.setVisible(true);
   }

   public TempAbout() {

       setLayout(new BorderLayout());
       JButton aboutButton1 = new JButton("About 1");
       aboutButton1.addActionListener(this);
       getContentPane().add(aboutButton1, BorderLayout.NORTH);

       JButton aboutButton2 = new JButton("About 2");
       aboutButton2.addActionListener(this);
       getContentPane().add(aboutButton2, BorderLayout.CENTER);

       JButton aboutButton3 = new JButton("About 3");
       aboutButton3.addActionListener(this);
       getContentPane().add(aboutButton3, BorderLayout.SOUTH);

   }

   public void actionPerformed(ActionEvent actionEvent) {

       String command = actionEvent.getActionCommand();
       if (command.equals("About 1")) {
           JOptionPane.showMessageDialog(null, "Message 1", "Title 1",
                   JOptionPane.INFORMATION_MESSAGE);
       } else if (command.equals("About 2")) {
           JOptionPane.showMessageDialog(null, "Message 2", "Title 2",
                   JOptionPane.INFORMATION_MESSAGE, null);
       } else if (command.equals("About 3")) {
           ImageIcon aboutIcon = null;
           URL aboutIconUrl = this.getClass().getClassLoader().getResource(
                   "Images/Duke.gif");
           if (aboutIconUrl == null) {
               System.out.println("Couldn't find icon file.");
           } else {
               /* convert URL to encoded String */
               String encodedAboutIconFileName = aboutIconUrl.getFile();
               String decodedAboutIconFileName = null;
               try {
                   decodedAboutIconFileName = URLDecoder.decode(
                           encodedAboutIconFileName, "UTF-8");
               } catch (UnsupportedEncodingException ue_excp) {
                   System.err.println("Failed to decode file name "
                           + encodedAboutIconFileName + ". Cannot
continue.");
                   System.exit(16);
               }
               aboutIcon = new ImageIcon(decodedAboutIconFileName);
           }

           JOptionPane.showMessageDialog(null, "Message 3", "Title 3",
                   JOptionPane.INFORMATION_MESSAGE, aboutIcon);
       }
   }
}