installing java on Linux

I have recently installed the Linux java RE rpm from Sun's website, or
at least I thought I did. after trying to run a java program I've
written, the command "java" could not be found. I tried the "which
java" command, which told me java was not installed. I made my way to
/usr/java, where the RE and SDK packages had all sorts of binary files
and system libraries. Unfortunately, I don't know where they all go,
although I thought the rpm would have taken care of that. A friend of
mine said I should install java "from scratch," but I don't know where
to start. Any suggestions?

+ David Huerta