Initially, the EV3 Lego robot is delivered with an operating system made by Lego, and one needs to use LEGO MINDSTORM software to program it. It is really easy to use this software and to program the robot; however, it uses a graphic programming language made for children or uninitiated people. This language proposes only basic functions and if one wants to use Bluetooth or a loudspeaker one has to implement another OS (Operating System) to have access to more specifics functions.
LeJOS is a firmware replacement for Lego Mindstorms programmable bricks. It can do a lot of things restricted by the initial OS, but there are a couple of things required before one can do the following:
In order to switch the Operating system on the robot, I found all information on the following web site: http://sourceforge.net/p/lejos/wiki/Home/
I will review what I did step by step:
1) Install the operating system: http://sourceforge.net/p/lejos/wiki/Windows%20Installation/
You only need to download the most recent version of LeJOS EV3 and follow instructions. The software will help you for the next step: Creating a bootable SD card
2) Creating a bootable SD card
For this part you need a MicroSD memory card with at least 2GB, then you will follow the instructions on the previous link.
3) Eclipse plugging installation:
To program the EV3 robot in java you will need an IDE(Integrated Development Environment).Eclipse is a good tool to program in java and you must have it to use LeJOS libraries.
4) Configuring the connection between robot and computer:
There is no driver with LeJOS, so you have to configure the device to make it compatible with your computer.
There are a lot of examples furnished with LejOS to help you get started.
You can also download all these projects with git:
Gti : git clone git://git.code.sf.net/p/lejos/ev3 lejos-ev3
help with GIT : windows : http://msysgit.github.io/