Lesson: Introduction

Introduction to Java programming on the EV3 platform using leJOS.

Understand the basic concepts of the leJOS software tool that enables Java on the EV3 as well as the use of the Eclipse IDE with the EV3.


We have been learning a lot about the Java programming language. Now its time to explore how we actually write, compile and deploy Java programs for the EV3 (FLL) robotics control system.

The EV3 robotics controller or "brick", does not support Java out of the box. However, a software toolset (SDK), called leJOS, provides a JVM for the EV3 that allows us to download and run Java programs on the EV3. Additionally, leJOS provides a rich library of Java classes (API) that provide access to the functions of the EV3 and the motors, sensors and other devices that can be attached to the EV3.

leJOS is installed on an SD memory card and that card is inserted into the EV3. When the SD card is inserted and the EV3 is turned on, it will start up or "boot" into the leJOS run time environment. This environment hosts your Java programs and lets you select which one you want to run and start it. It also allows for configuration of EV3 and leJOS features. When the SD card is not inserted, the EV3 will start up in the standard EV3 run time environment.

To develop programs for the EV3, we will need to install the Java SDK on your PC and the leJOS SDK. We describe how that is done in the next lesson.

We also need an Interactive Development Environment in which to create, compile and deploy our programs. For the EV3 with leJOS, the IDE is Eclipse. Eclipse is a standard IDE used with many programing languages and hardware platforms. leJOS contains an Eclipse "plugin" which gives Eclipse special features that make it easy to develop and deploy programs to the EV3. We will cover installing Eclipse shortly.

When all of these components are installed we will be ready to look at actual EV3 programming using Java.

You can learn more about leJOS here and in the excellent reference/tutorial book Maximum Lego EV3 by Brian Bagnall (ISBN 978-0-9868322-9-1).


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