Question on Menu listener de selection

Question

Hi,
I got an exception Exception in thread "AWT-EventQueue-0" while running the below program, please explain why this exception is coming.
Select the count menu and then deselect it an exception is occuring how to solve this, and explain what is the reason for the exception raising.
import java.awt.*;
import javax.swing.*;
import javax.swing.event.*;
public class allframes {
     JFrame frame=new JFrame("Hello World");
     JDesktopPane pane;
public static void main(String[] args) {
     new allframes();
public allframes(){
     pane=new JDesktopPane();
     try{
          String str=JOptionPane.showInputDialog("Enter the Number of frames");
          int j=Integer.parseInt(str);
          for (int i = 1; i < j; i++) {
               JInternalFrame iframe=new JInternalFrame("Frame"+i,true,true,true,true);
               iframe.setBounds(i*20,i*20,150,100);
               pane.add(iframe);
               iframe.setVisible(true);
               iframe.setToolTipText("Frame"+i);
     catch(Exception e){
          JOptionPane.showMessageDialog(null,"Enter a valid no");
          System.exit(0);
     JMenuBar bar=new JMenuBar();
     JMenu menu=new JMenu("Count");
     JMenuItem item=new JMenuItem("Hello");
     JMenuItem item2=new JMenuItem("Raja");
     menu.addMenuListener(new hi());
     menu.add(item);
     menu.add(item2);
     bar.add(menu);
     frame.add(pane);
     frame.setJMenuBar(bar);
     frame.setSize(600,600);
     frame.setVisible(true);
     frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
class hi implements MenuListener{
     public void menuSelected(MenuEvent e){
          int k=pane.getAllFrames().length;
          JOptionPane.showMessageDialog(null,"the no of frames are"+k);
//          int n = JOptionPane.showConfirmDialog(null,"sel  message");
//          System.out.println("sel " + n);
     public void menuDeselected(MenuEvent e){
          JOptionPane.showMessageDialog(pane,"Menu is deselected");
          System.out.println("desel");
//          int n = JOptionPane.showConfirmDialog(null,"de sel  message");
//          System.out.println("sel " + n);
     public void menuCanceled(MenuEvent e){
           JOptionPane.showMessageDialog(null,"Menu is canceled");
//          System.out.println("sel " + n);
}Edited by: RajivGuna on May 18, 2011 12:04 PM

Answer 1

It doesn't like the JOptionPane. When the option pane closes I think it tries to set focus back on the popup menu. However, the component is no longer visible. Get rid of the option pane.
Or you can wrap the code in an invokeLater:
SwingUtilities.invokeLater(new Runnable()
     public void run()
          JOptionPane.showMessageDialog(pane ,"Menu is deselected");
});