I too like VI but for large projects it's slow.

Being able to jump from one source to another saves tons of time, as do things like code completion (type the first few characters and a list of available methods and members starting with that is presented).

Also, having realtime syntax checking in Eclipse has almost done away with compiler errors for me.

All of those of course should only be used once you know the language. To LEARN Java something like VI is best.
To use it professionally use whatever is available, having a strong IDE like Eclipse will increase your productivity a lot.

I just bought the Java 2 for dummies book to help with my Java course, it came with an IDE called JCreator - its great i highly recommend it if your a beginner, not too simple, not too complex. I have tried Eclipse and NetBeans but they were too complicated to set up i found.