Question: How can I tell what version of Java I'm using?
You can actually do different things on different platforms to figure out which version of Java you're using, and which versions of Java may be installed, but the one cross-platform (Unix, Linux, Mac OS X, Windows) thing you can do is open up a command-line window (a terminal on Unix and Mac, a Command windows on Windows) and type this command:
On my current Mac OS X version (10.4.10) the output from this command looks like this:
java version "1.5.0_07" Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0_07-164) Java HotSpot(TM) Client VM (build 1.5.0_07-87, mixed mode, sharing)
This shows that I'm using Java version 1.5, or more specifically, version 1.5.0_07.