FocusLost event on same component generated multiple times... why?

Question

This is a reiteration of the topic of a post from Jan. 2006 by Toxter.
Although Toxter got his problem resolved, the question of the title of his post (same as mine) was never answered.
Suppose you want to validate text of a component (say, a JTextField) by checking the text when the component loses focus, by implementing the focusLost method in a FocusListener. The listener catches focusLost events from the given component and does validation and if found invalid, opens a warning dialog (say, a JOptionPane). Suppose further that in your implementation of the focusLost method, after returning from the JOptionPane call, you call requestFocusInWindow() on the JTextField so the user can make the correction straight-away. What happens, weirdly, is that you get multiple recurrences of a focusLost event from the very same textfield component, generating multiple JOptionPane popups, before the user is actually able to access the textfield and make a correction.
No reason was given as to why this happens. Toxter reported that focusLost would get called twice. I routinely get 3 occurrences.
In any case, why does this happen?
There are at least a couple of other workarounds besides the one accepted by Toxter:
1) you can drop the call to textField.requestFocusInWindow... without that call you don't get multiple occurrences of focusLost FocusEvents
2) you can wrap the call to requestFocusInWindow in a call to SwingUtilities.invokeLater (within the run method of an anonymous Runnable):
     if( !validatePositiveIntegerField(txtFld) )
         JOptionPane.showMessageDialog(this, INPUT_ERR_MSG,
                  INVALID_ENTRY_TITLE, JOptionPane.WARNING_MESSAGE);
         SwingUtilities.invokeLater(new Runnable()
            public void run()
               txtFld.requestFocusInWindow();
      }Workarounds are great but it's nice to understand the underlying causes of problems too... If anyone (Toxter, do you know?) can give even just a brief nutshell explanation as to why this occurs, I'd like to hear it.
Thanks in advance.

Answer 1

Use an InputVerifier:
http://forum.java.sun.com/thread.jspa?forumID=57&threa
dID=776107&start=6Thanks for the reply, camickr. Several workarounds were already noted. That wasn't the question. The question was: what is the underlying cause of the multiple occurrences of focusLost events from the given JTextField which cause the JOptionPane to pop up multiple times? On the face of it, it seems to be a bug in how focus events are getting generated. Here is a bit of code that will generate the problem:
   public void focusLost(FocusEvent e)
      if( e.getSource() == txtFld && !validatePositiveIntegerField(txtFld) )
         JOptionPane.showMessageDialog(this, INPUT_ERR_MSG, INVALID_ENTRY_TITLE,
                                       JOptionPane.WARNING_MESSAGE);
         txtFld.requestFocusInWindow();
   }In my previous post, I pointed out that the multiple focusLost events can be avoided if one either drops the call to txtFld.requestFocusInWindow() altogether, or else wraps that call in the run method of a Runnable executed with SwingUtilities.invokeLater. But the question I posed was, why is the code above causing multiple occurrences of focusLost events from the txtFld component?
Any help in getting an explanation of that seemingly buggy behavior would be appreciated.
Cheers