This week's book giveaway is in the OCPJP forum. We're giving away four copies of OCA/OCP Java SE 7 Programmer I & II Study Guide and have Kathy Sierra & Bert Bates on-line! See this thread for details.
It is quite easy to put keys or values into a Map, but you need to put them in pairs. If your elements from the Map go as Keys, what would you use as Values? If your elements from the Map go as Values, what would you use as Keys?