[java4first]

And to answer the original question(s):

If you look on page 80 in the "Getting Started with the 2016 Control System", it will have a table of software and firmware numbers. The last two are for the RoboRIO firmware and the RoboRIO Image. If you have gotten those updated correctly following the instructions, the web browser admin page should show those version numbers on it (along with everything else).

To check that you have the right Java installed, ssh to your roboRIO and run the following: /usr/local/frc/JRE/bin/java -version and it should come back with what you picked from the Oracle site (probably 1.8.0_06).

WPILib just released a new version with the Update 2 package, and if you have this installed correctly, and go to (in Eclipse) Help -> About and then Select Installation Details. You should see the WPILib Java (or C++, I suppose) at 0.1.0.201601151923.

If all that lines up, and you are still getting the 23 error - deleting the built "wpilib" folder while Eclipse is closed, re-starting Eclipse and rebuilding the project to recreate it should work - at least it did for me.