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e767. Determining When the Menu of a JComboBox Component Is Displayed

    // Create component
    String[] items = {"item1", "item2"};
    JComboBox cb = new JComboBox(items);
    cb.setEditable(true);
    
    // Create and register listener
    MyPopupMenuListener actionListener = new MyPopupMenuListener();
    cb.addPopupMenuListener(actionListener);
    
    class MyPopupMenuListener implements PopupMenuListener {
        // This method is called just before the menu becomes visible
        public void popupMenuWillBecomeVisible(PopupMenuEvent evt) {
            JComboBox cb = (JComboBox)evt.getSource();
        }
    
        // This method is called just before the menu becomes hidden
        public void popupMenuWillBecomeInvisible(PopupMenuEvent evt) {
            JComboBox cb = (JComboBox)evt.getSource();
        }
    
        // This method is called when menu is hidden because the user cancelled it
        public void popupMenuCanceled(PopupMenuEvent evt) {
            JComboBox cb = (JComboBox)evt.getSource();
        }
    }