A.Jorge Garcia:

http://java.sun.com is where you can download the Sun JDK. It comes with the JVM too.
http://www.blackdown.org is where you can download the Blackdown port of the JDK.

The beauty of Linux is you can install as many JDK/JVM that you want and all you need to do is set the JDK_HOME variable and the PATH variable to point to the correct location and you're set.

I'd ditch gcj for now as the performance I get from Blackdown is good.