Determining the version of Java SDK on the Mac

In /System/Library/Frameworks/JavaVM.framework/Versions you'll see all the installed JDKs. There is a symbolic link named CurrentJDK pointing the active JDK.

Open a terminal and type: java -version, or javac -version.

If you have all the latest updates for Snow Leopard, you should be running JDK 1.6.0_20 at this moment (the same as Oracle's current JDK version).