MINDSTORMS NXT with JAVA
A guide to getting started
Berry Nall
Robotics Coach, Roma High School
I. Introduction
What is leJOS?

“leJOS NXJ is a Java programming
environment for the LEGO MINDSTORMS
NXT ®. It allows you to program LEGO ®
robots in Java.”
http://lejos.sourceforge.net/nxt/nxj/tutorial/Preliminaries/Intro.htm
Why would educators use leJOS?



Introduce students to text-based
programming
Inspire student interest in JAVA, a widelyused programming language
Allow students to take advantage of leJOS’
superior performance
At the 2011-12 TCEA Region One Advanced Arena competition, the top 3 robots
and at least 4 of the top 6 finishers were programmed using text-based
programming (leJOS or RobotC).
Other Advantages of leJOS
(compared to NXT)





Faster loading and program execution
Programs use less memory
Greater accuracy
Scalable
Free!
Who can learn to use leJOS?


Anyone here (and your students) can learn
enough to program for a TCEA competition.
We hope some of our students will go far
beyond what we can do.
II. Eclipse IDE
An Integrated Development Environment is a program
that allows you to write (and run) programs.
Uploading leJOS to the brick
If something goes wrong?



The brick will most likely make a ticking
noise.
1. Reinstall the NXJ software using the
LEGO-supplied program.
2. Upload the leJOS software again.
Exploring Eclipse
Upload program
Locate program files
Edit program
Upload status
Eclipse helps


In Eclipse, the view is called a “perspective.” Students may change it
accidentally, causing confusion.
This view is saved as the “leJOS” perspective.
Current perspective

To restore, click “Window”, then choose “Reset
perspective”
Eclipse helps

Eclipse tells you if there is a typing error or an
illegal command:
Eclipse helps

Click here to load a program:
III. JAVA basics
JAVA Rules to remember

Capitalization matters! Ex: tcea is not
TCEA is not tCeA


Every command ends with a semicolon
// means you are inserting a comment;
everything after the slashes is ignored
IV. Writing programs
Program Sections
Import
statements






File name



Define pilot,
sensors

import lejos.nxt.*;
import lejos.robotics.navigation.*;
import lejos.util.Stopwatch;
/**
*comment to name author (please change!)
*
*/
public class TCEA
{
//Variables and declarations go here

public static void main(String[] args)
{
// program goes here

}


Commands
for robot to
follow

}
To start: modify TCEA.java for your
robot



Experimentally determine the wheel diameter.
Make the “travel” statement a comment and
remove the comment slashes from the “rotate”
statement.
Experimentally determine the wheel base. Note:
the wheel base may need to be modified for
different surfaces or designs even if the actual
size doesn’t change.
Test your robot:
TCEA1rectangle.java

If the wheel diameter and wheelbase are
set correctly, the robot will travel in a
rectangle and arrive where it started.
To program your robot: save the
modified TCEA.java with a new name.


Change the class to the name of your file.
Add commands to make the robot move.