How do I run JOptionPane on EDT?

Question

I'm still having problems with blank JOptionPanes. Based on research at SO and in Java Docs, this obviously has something to do with not using the EDT. My question is how exactly do the EDT and its methods apply to JOptionPane? For example, the terminal error output makes it quite clear that the JOptionPane below is not run on the EDT. What's missing specifically, and how does something like Runnable fit in?

import javax.swing.*;
public class PaneDemo
{
public static void main(String[] args)
{
    final String[] TEXT ={
            //message
            "Hello, World!",
            //title
            "Greeting"};//end TEXT
    showMyPane(TEXT);
}//end main
public static void showMyPane(final String[] TEXT)
{
    JOptionPane.showMessageDialog(null, TEXT[0], TEXT[1], 
        JOptionPane.INFORMATION_MESSAGE);
    if(!SwingUtilities.isEventDispatchThread())
    {
        System.err.println("Err: GUI failed to use EDT.");
    }//end if(!SwingUtilities.isEventDispatchThread())
}//end showMyPane
}//end class PaneDemo

An answer suggested adding invokeLater. That doesn't seem to render very well in BlueJ, however.

Also isEventDispatchThread() is still returning the error in the terminal. Is that simply because it is now in the wrong location?

Answer 1

You can create JOptionPane on the Event Dispatch Thread like this:

  final String[] TEXT = {
        //message
        "Hello, World!",
        //title
        "Greeting"};//end TEXT

     ...

    /**
     * Create GUI and components on Event-Dispatch-Thread
     */
    javax.swing.SwingUtilities.invokeLater(new Runnable() {
        @Override
        public void run() {
                JOptionPane.showMessageDialog(null, TEXT[0] 
                      + "\n is on EDT: " + SwingUtilities.isEventDispatchThread(), TEXT[1],
                        JOptionPane.INFORMATION_MESSAGE);
        }
    });

Have a look at the Lesson: Concurrency in Swing it should help you understand what its all about

UPDATE:

as per comment you should initiate the JOptionPane on the EDT on each call in showPane(...) method like so:

   public static void showMyPane(final String[] TEXT) {
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                JOptionPane.showMessageDialog(null, TEXT[0] 
                      + "\n is on EDT: " + SwingUtilities.isEventDispatchThread(), TEXT[1],
                        JOptionPane.INFORMATION_MESSAGE);
            }
        });
    }//end showMyPane

    public static void main(String[] args) {
        final String[] TEXT = {
            //message
            "Hello, World!",
            //title
            "Greeting"};//end TEXT
        showMyPane(TEXT);
    }