Lesson: Installing leJOS

Installation procedure for leJOS and Java.

Install leJOS and the Java SDK on your PC. Create the SD memory card for the EV3 brick.


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 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. Later, when you install leJOS, 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 between 2GB and 32GB in size and not SDXC. Do not use a smaller or larger size. 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.


Lesson navigation: