While you can certainly get started right away with the built-in Java mode, if you do more than occasional Java programming, you might want to venture into the world of Paul Kinnucan's Java Development Environment for Emacs (JDEE). It takes Emacs into the realm of Java IDE. You won't find a GUI builder, but everything else is in place and ready to roll.
You can pick up the latest version of the JDEE online from http://jdee.sunsite.dk/. This site is essential to getting the JDEE up and running. You'll find all sorts of tips and tricks and full user documentation on all of the bells and whistles is available.
Before you can install the JDEE, you'll need the following components:
Available on SourceForge (http://cedet.sourceforge.net/) or by following the links from the JDEE home page. This collection is quite popular as a foundation for more interesting programmer tools. You may already have a sufficient version installed, but it's best to get the latest release.
Available as a separate download from the JDEE site.
While technically not required for editing files in Emacs, a JDK is required to take advantage of any of the compilation or debugging features of the JDEE. You'll also have to register each JDK you plan to use, but more on that later.
Installing CEDET is fairly straightforward if you have ...