I gave a shot to GCJ to do a tiny project. At the first place I thought the official Sun JDK was bulky and I preferred a lightweight Java SDK. But it turned out that the debugger for GCJ was almost unable to use. I was unable even to inspect an array. So switched to the official JDK and used JDB in Emacs(binding step-in, step-next to F7/F8). I was quite happy with it. I think for any Java novice, JDK is the way to go.