Try /usr/bin/java -version
or simply java -version
if it comes back with
Kaffe Virtual Machine
Copyright (c) 1996-2000
Transvirtual Technologies, Inc. All rights reserved
Engine: Just-in-time v3 Version: 1.0.6 Java Version: 1.1
or perhaps Blackdown 1.1.8 or even IBM 1.1.8 then its time to visit
to download the latest J2SE which is now v1.4
note since this is 40Mb this is for people with broadband connections.
Actually 1.1 versions are okay for learning basic java , 1.2 was a significant upgrade incorporating the swing user interface amongst other things, 1.3 wasn't as big a leap as 1.2, but 1.4 is another big leap introducing many new features.
for the record
java version "1.4.0"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.0-b92)
Java HotSpot(TM) Client VM (build 1.4.0-b92, mixed mode)