The easiest way to set up communication between the computer and the robot is to use the communication classes included in the leJOS PC library.
The computer side project (the one that reads from the controller) should be set up according to
these instructions. Then you can use DataOutputStream (on the computer) and DataInputStream (on the robot) to send numbers over bluetooth. I would recommend using USB for testing as it is more reliable and faster to connect and the APIs are nearly identical.
These instructions might help with setting up communications.
I also have some more complicated communication code that you can look at if you want. This provides a way for bidirectional communication that is sort of similar to I2C. There are a few intermittent threading bugs, but it might give you some idea of how to connect the computer and the robot.
Computer Code
Robot Code
Feel free to ask any other questions you have about the specifics of getting your leJOS working.