Using 'Alternatives' in Linux to use a different Java package

Installing Sun Java alongside the default GNU java using the 'alternatives' system.
This post shows how to install Sun's java implementation alongside the Linux default GNU java.

Installing Sun Java alongside the default GNU java
Sun's java isn't installed by default on RedHat systems. This is because Sun hasn't licensed it for RedHat's distribution. Instead, Linux ships with an open source alternative, GNU Java. It's based on Sun's Java implementation, and--in part because of that--it's always a version or two behind Sun. In all, it's a very good implementation, but sometimes--as in the case with DSpace--it's necessary to use Sun's Java, instead.
We don't want to remove the Gnu Java; we'll install Sun's alongside it.