Lesson: Installing leJOS

There are three main steps to installing leJOS. The first two steps are installing the Java and leJOS SDKs on your PC. The third step is creating the leJOS memory card that goes in the EV3. This three part installation process for Windows (Mac users see below) is documented on the leJOS web site here. Open the link and follow the instructions, after reading the following three notes:

Note: Be sure to first install the Java SDK (called JDK) version 7 (1.7) if not already installed on your PC. Install and use version 7 even if you have version 8 or later installed. JDK 7 is now in archive state at Oracle. You can download jdk-7u80-windows-i586.exe here. Oracle requires you to create an account to download. When installing, you only need the Development Tools, you can X out Source Code and Public JRE. After this, when you install leJOS with the instructions above, the installer will ask for the location of the JDK you wish to use. Select the folder where JDK 7 was installed. This is typically C:\Program Files (x86 if 64-bit Windows)\Java\jdk1.7.0_80.

Note: The memory card is a micro-SD card and must be larger than 2GB and less than 32GB in size and not SDXC. You may need a micro-SD adapter (sold with most micro-SD cards) to insert the micro-SD into your PC. Be sure you have the card and adapter (if needed) before starting the installation. Read the instructions for running the SD card formatting utility carefully. You will need to download the Java 7 JRE in zipped form per those instructions so it can be transferred to the SD card.

Note: The first time you boot the micro-SD card on an EV3, leJOS will perform an installation process on the card. This will take 10-12 minutes to complete.

After installing leJOS, the documentation for the leJOS EV3 Java API is located at:

C:\Program Files\leJOS EV3\docs\ev3\index.html.

You should open this file in your browser and bookmark it.  You will need this documentation to explore and use the leJOS EV3 classes in your programs.

Installation instructions for Mac are similar and are located here. Note: In step 6.7 of those instructions, you are told to download version 8 of the JRE. However if you look at the picture of the download site, you will see that version 7 is highlighted. Be sure to select version 7.