I'm currently using Ubuntu Linux, and I can use gij to run .class files just fine. However, I'm unaware of how to compile .java files into .class files from the command line. Is there similarly a simple way to do this, such as a gij option or parameter?

You need gcj. You should be able to install it with synaptic.

Here's a blurb from the website

Quote: GCJ is a portable, optimizing, ahead-of-time compiler for the Java Programming Language. It can compile:

* Java source code directly to native machine code,
* Java source code to Java bytecode (class files),
* and Java bytecode to native machine code.

Alternatively you can download a compiler directly from Sun. IIRC there's some info about this somewhere in the ubuntu wiki.