The main classes are JGEngine (the whole game) and JGObject (a sprite object). Sublass these to write your own game. It's handy to have your JGObject classes as inner classes of your JGengine. JGTimer is used for creating timers in your games. ImageUtil contains some stand-alone image manipulation methods.

StdGame is a game framework that handles a standard game state machine (startlevel, life lost, game over, etc). It is built as a layer on top of JGEngine.

JGame should also come with a user manual (the file MANUAL). It is distributed under the revised BSD license (see the file LICENSE). More information can be found on the website, http://www.13thmonkey.org/~boris/jgame/