One of the nicest features of Eclipse is it’s tools for searching through a large complex project. Even if you don’t use Eclipse as your main IDE it is worth loading your code into Eclipse so that when you are asked the inevitable questions about what a particular piece of code does (or more often and harder to answer still, which piece of code does what) you can dive right in and let Eclipse guide to the answer.
Eclipse 3.2 turbo charges the existing functionality as far as I am concerned. It already had a powerful regular expression matching but this improved now with a split list of likely matches coming before a broader list. It is also incredibly fast, even for a huge legacy application. As far as I’m concerned Eclipse is the number one Java source browser around at the moment.