Being a DBA who supports Java Developers, I try understand a little about Java. When recently trying to determine what version of Java was installed on a server, I found Java Tester while searching with Google.
Navigating to the Java Version link, I was able to find my answer. There is other good basic Java information found on the web site.
Answer to finding JDK location on Windows or Unix at Stackoverflow.
Also for finding the Java version, you can also run the command below:
C:\> java -version
java version "1.6.0_29"
Java(TM) SE Runtime Environment (build 1.6.0_29-b11)
Java HotSpot(TM) Client VM (build 20.4-b02, mixed mode, sharing)