This week's giveaway is in the EJB and other Java EE Technologies forum. We're giving away four copies of EJB 3 in Action and have Debu Panda, Reza Rahman, Ryan Cuprak, and Michael Remijan on-line! See this thread for details.
I don't think it is possible to find out which JDK was used for compiling. What *is* possible (and what that linked page shows) is which JRE the class was compiled *for* (which is, of course, the more useful thing to know).
Ping & DNS - updated with new look and Ping home screen widget