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Jeroo built on top of GridWorld for teaching computer science
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GWJeroo is a library that lets students run Jeroo programs in GridWorld. GWJeroo is intended for students in Pre-AP and AP classes who are transitioning from Jeroo to Java.

I developed this in 2007 when I was a high school computer science teacher. I no longer teach, so I don't expect to update it.


  • GWJeroo code looks almost identical to Jeroo code.
  • GWJeroo can use any feature in the Java language including variables, for loops, and out.println().
  • GWJeroo is just a standard Java library that is distributed in a jar file. It compiles and runs in any normal Java IDE.
  • When a GWJeroo program runs, students run their program one line at a time using Gridworld's step button.
  • GWJeroo can read .jev files from Jeroo.
  • In GWJeroo, the class Jeroo extends the class Actor. This means you can call any of Actor's methods, such as setColor() or moveTo() (But I don't plan on telling my students this too quickly. (Things like moveTo() make some problems too easy!))
  • The island can have any number of Jeroos. You can also have multiple classes that extend Jeroo, so you can have different types of Jeroos.


To use GWJeroo, you need to put the file gwjeroo.jar in the classpath. This is the only file from this project that students will need.

Getting Started

I have included three sample programs to help you get started:

  • - This is the solution to the Look Homeward Angel from the original Jeroo worked in GWJeroo. It demonstrates how similar they are, and shows how to load a jev file.

  • - This is a more complex example that shows how to create a new type of Jeroo. You have to create a subclass of Jeroo to create new methods.

  • - After you have been teaching Java for a while, you can go back to this one. It is intended to teach creating accessors and modifier methods. Here's the story: a bunch of Jeroos are going to the prom and they are looking for dates. They wander around aimlessly until they run in to someone that meets their standards. As the Jeroos wander, they lower their standards. Students generate some interesting bugs while solving this problem.

Sample Code

To give you a better idea of how GWJeroo compares with Jeroo, here is some sample code:

Code in JerooCode in GWJeroo
The Main Method
method main() {
    Jeroo kim = new Jeroo();


public static void main(String[] args) {
JerooWorld world = new JerooWorld();
ExtendedJeroo kim = new ExtendedJeroo();
world.add(new Location(0,0),kim);;



A Jeroo Method
method turnAndGo() {
public void turnAndGo() {
Calling a constructor
method main() {
Jeroo kim = new Jeroo(3,4,EAST,100);
import info.gridworld.grid.Location;

public class ExtendedJeroo extends Jeroo { public ExtendedJeroo() { super(EAST,100); } public static void main(String[] args) { JerooWorld world = new JerooWorld(); ExtendedJeroo kim = new ExtendedJeroo(); world.add(new Location(3,4),kim);; kim.hop(); } }

After, code can be copied directly from existing main methods into GWJeroo methods. You can copy and paste Jeroo methods to GWJeroo by changing the word method to "public void". The one place where GWJeroo is significantly different from Jeroo is when you need to create a Jeroo using a constructor other than the default constructor.


Here's some assignments and resources other people created for GWJeroo: and .

I made a few small changes to the original GridWorld source code. They are documented in the file gridworld.diff .

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