JComboBox - delaying the dropdown list

Question

Does anyone know how to delay the population of a JComboBox's list until the user clicks the down arrow?
In effect:
1) the user clicks the arrow on the comboBox
2) the wait cursor appears (no drop-down yet)
3) the list gets built (still no drop-down)
4) the data retrieval is done, the drop-down list is then shown, and the cursor returns to normal

Answer 1

The size of the popup is based on the number of elements in the
combobox before the model was rebuilt. We need to reset the popup
when the number of items in the combobox changes.That seemed to do the trick. I don't know what I was trying originally before I posted for help, but when I called hidePopup() or showPopup() from within the popupMenuWillBecomeVisible() method, I was getting a stacktrace out the wazoo.
Thanks for all of the ideas. Here's a completed example in case someone wants to refer to this later. I even added a sleep() call in the rebuildList method to simulate a long transaction, so that you can see the effect of the delay:
import java.awt.*;
import java.awt.event.*;
import java.util.*;
import javax.swing.*;
import javax.swing.event.*;
public class DelayedComboBoxTest extends JFrame
  private JCheckBox chkA = new JCheckBox("A");
  private JCheckBox chkB = new JCheckBox("B");
  private JCheckBox chkC = new JCheckBox("C");
  private JComboBox cboItems = new JComboBox();
  public DelayedComboBoxTest()
    super("Delayed ComboBox Test");
    setDefaultCloseOperation(EXIT_ON_CLOSE);
    JPanel p = new JPanel();
    p.add(chkA);
    p.add(chkB);
    p.add(chkC);
    p.add(cboItems);
    Container c = getContentPane();
    c.setLayout(new BorderLayout());
    c.add(p);
    pack();
    cboItems.addPopupMenuListener(new MyPopupMenuListener());
  private void rebuildList()
    setCursor(Cursor.getPredefinedCursor(Cursor.WAIT_CURSOR));
    Vector items = new Vector();
    if (chkA.isSelected()) { items.add("A"); }
    if (chkB.isSelected()) { items.add("B"); }
    if (chkC.isSelected()) { items.add("C"); }
    cboItems.setModel(new DefaultComboBoxModel(items));
    try
      new Thread().sleep(1500); // simulate a long transaction
    catch (InterruptedException ex) {}
    setCursor(Cursor.getPredefinedCursor(Cursor.DEFAULT_CURSOR));
  public static void main(String[] args)
    JFrame f = new DelayedComboBoxTest();
    f.setVisible(true);
  class MyPopupMenuListener implements PopupMenuListener
    public void popupMenuCanceled(PopupMenuEvent e) {}
    public void popupMenuWillBecomeInvisible(PopupMenuEvent e) {}
    public void popupMenuWillBecomeVisible(PopupMenuEvent e)
      int items = cboItems.getItemCount();
      rebuildList();
      if (items != cboItems.getItemCount())
        cboItems.hidePopup();
        cboItems.showPopup();
}One downside though: typically, a change in one of the trigger fields' content (the 3 checkboxes in this case) would cause the list to be rebuilt. It's there where you can check to see if the previously selected item in the list is contained in the new list. If so, reselect it, otherwise clear the selection. In other words, if the old value is still valid, keep it selected.
In this new way, the old value remains selected even if it's logically bad. On save, one would have to query if the selected value is still valid based on the criteria of the other trigger fields. Yeah, it's an extra step, but I don't mind doing an inexpensive hit once (on save) rather than an expensive one several times as each of the trigger fields is changed (of which could be many)