Java is designed to share code and work in groups. The object oriented nature of Java means someone can use your code without having to know anything about how it works. They just have to know how to interface with it. This makes breaking large coding projects up into smaller pieces much easier. 

Partner up with 1-3 other students in class. Come up with a program that you want to work. Divide up the work and start programming. 

See the APCS Games Page for ideas if your group cannot think of anything.