This week's book giveaway is in the General Computing forum. We're giving away four copies of Arduino in Action and have Martin Evans, Joshua Noble, and Jordan Hochenbaum on-line! See this thread for details.
I guess you can add a FocusListener to the text field. When the focusLost() event is fired you get the source which will be the text field and then get the parent which should be the popup menu which you can then hide manually.