This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori 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).