BlueJ is an interactive Java development environment. It provides a unique user interface that presents a graphical display of the application classes and their relationships, and it lets users interactively create objects of any class. Once objects have been created, users can interact with them directly. This interaction mechanism allows for much greater testing and experimentation than in conventional environments. BlueJ is suited for teaching and learning OO and Java.
Greenfoot is an integrated development environment that makes it easy to write games and simulations in Java. It comes with a broad range of demo scenarios and documentation that gets newcomers started very quickly. Greenfoot may be used to learn or teach programming, or just to write a cool game and maybe put it up on a Web site. (it can export the game to a Web page). It was originally developed for school age learners, but is now used by all age groups.