I think a DocumentListener is your best bet. You should be able to detect actual 'edit' type actions by the user. If you less demanding in what you interpret as an 'edit', then a combination of KeyListener and MouseListener might be easier to figure, but they would fire when anything happens inside the field, whether anything was changed or not.
Tim
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"Your morbid fear of losing,
destroys the lives you're using." - Ozzy