One of the nicest things about Mac OS X is its very broad range of tools. The Classic Mac OS platform had many software development tools, of which the most popular and flexible was Metrowerks CodeWarrior. The release of Mac OS X, however, has broadened the range of available tools tremendously, and a large set of Java- and Unix-based tools is now available. Mac OS X also ships with Project Builder, an integrated desktop environment for programming in several languages, including Java.
It's worth taking the time to review the various tools. If you're an old emacs or vi hand, you'll be able to access those tools (just fire up the Terminal). Even if you're an emacs or vi addict, you still might want to browse through the tools just to get an idea of what folks are talking about.