It's not too hard... you can even do it yourself! All you need are a few classes...
Actor, to hold player information
Level, to hold information about the terrain
Barrier, which represents something the character cannot walk onto
Game, extends JApplet and contains the whole thing
Item, used for powerups
AIController, for attaching onto an Actor to create enemies
You can subclass any or all of these if you want to take it further. I made my first RPG in about a week for an English assignment. CAUTION: IT STINKS but that's only because I didn't take the time to polish it. You can find it on my website www.freewebs.com/kingdomofnerd
If you go to the Downloads page, download Deathwatch.zip, and open it, you can see just the tip of the iceberg of what you can do.
Suggestions: You can create a cutscene class to represent character dialogue.
An interface defined to set and move locations of objects in your world might help too.