This week's book giveaway is in the Mac OS forum. We're giving away four copies of a choice of "Take Control of Upgrading to Yosemite" or "Take Control of Automating Your Mac" and have Joe Kissell on-line! See this thread for details.
I don't think there is any direct way to do that but you can add a listener to the list (addListSelectionListener) that's notified each time a change to the selection occurs.In case user selects more than three you can call clearSelection() to change the selection to empty set.
Snigdha<br />Sun Certified Programmer for the Java™ 2 Platform