Abstract

Advanced Placement courses in Computer Science are currently using a case study named GridWorld that provides a fun and exciting visual environment where young people can "program" the behaviors of objects within a virtual world. This workshop will introduce GridWorld and demonstrate its suitability to motivate early involvement of young people to conduct research through simulation and modeling.

Flow of Workshop

• Our CS1 Background
• Reference Links for Workshop
• Introduction to GridWorld
• GridWorld Tools for Research
• A GridWorld Start in Research
• A CS1 Class Research(ish) Assignment
• Visualization of Queueing Models
• Thankyou!!

Our CS1 Background

• Bob
• Teaching CS1/CS2 approximately 20 years
• APCS Reader for 2 year
• Laurie
• Teaching CS1/CS2 approximately 25 years
• APCS Reader for 18 years
• Head of the APCS Development Committee
• We've both experimented with other "fun" things in CS-1, such as Alice, RoboCode, Greenfoot, and Karel the Robot.
• We started teaching with GridWorld in Spring 2007. We recently observed students using GridWorld as a visualization tool in some simple research.

Reference Links for Workshop

• AP Central's GridWorld:
  • http://apcentral.collegeboard.com/
• GridWorld Online Reference:
  • GridWorld javadoc
• This Presentation Online:
  • http://eagle.cs.mercer.edu/CUR08
• Zip Folder of our Examples:
  • http://eagle.cs.mercer.edu/CUR08/gw.zip
• Sun's Java:
  • http://www.java.com/en/download/

Introduction to GridWorld

GridWorld consists of a "Grid" which is made up of "Locations." Each location can hold an "Actor." Each actor has a method named "act()" that is called by the Grid for each "Step." The Grid, Actor, Location and much more is all stored in the gridworld.jar. Confused? Lets take a look.

• Simple "Bug" example.
• A smarter Bug named "BoxBug."
• Hands-on: You get to make a "CircleBug!"

Introduction to GridWorld - Hands-on

You get to make a CircleBug!!!! A simple CircleBug would alternate between just moving and turning-and-moving on each call to act().

• Open the Bugs folder.
• Edit the CircleBug.java file.
• Create an instance variable to help alternate the behavior.
• In the Constructor, initialize the instance variable.
• In the act() method, alternate moving and turning-and-moving.
• Save it, and then run "runCircleBugRunner".

Tools for Research

GridWorld was not designed for conducting research. It provides introductory students with a visualization tool for representing things in the world. The following tools can help students begin experimenting and conducting some simple research.

• Visualizing Mathematical Distributions
      - Uniform,
      - Normal and
      - Exponential Distributions
• A GridWorld "Print String"
• Hands-on: Let's Roll Dice!

Tools for Research - Hands-on

Let's Roll Dice! First, lets look at rollDice.java which just randomly rolls 1-5 die (command line argument). Your job is to create a Java program that rolls the dice a large number of times and reports the frequency of each dice face that appears.

• Open the Distribution folder.
• Edit countDice.java.
• Add code to count the random die rolls (see comments)
• Add code to display the count of each dice face (see comments)
• Save it, and then run "runCountDice".

A Start in Research

In the spring of 2008 we had two students in our CS1 course that were highly motivated by GridWorld. One started by making a pet mouse and modeling some mouse behavior. Another student saw the mouse and researched maze generation.

• Pet Mouse
• Pet Mice
• Maze Generator
• Mouse in Maze
• Hands-on: Mouse eats cheese.

A Start in Research - Hands-on

Mouse eats cheese. You are going to let the mouse behave just like in PetMouse, except for when it finds cheese. Once there is cheese in front of a mouse, it will not move anymore (looks like it is eating the cheese).

• Open the PetMouse folder.
• Edit HungryMouse.java
• Leave canMove() and move() alone.
• In act() only move() if cheese is not in front of you. I'll give hints.
• Save and then run "runFeedMice"

A CS1 Class Research(ish) Assignment

A primary use of computer programs is to perform simulations. For this program, you will create a simulation of disease moving through a population. To do this, you will build three new objects that extend the Actor object. The complete assignment.

• Participant: this is similar to a Bug, except it moves left, right, or straight ahead at random, if the direction is not blocked.
• Subject: This is a Participant that can get infected. It will have a percentage chance of getting infected when it meets another infected Subject and a percentage chance of dying from the infection.
• Healer: This is a Participant that can heal infected participants. It will have a percentage chance of healing Subjects.

Visualization of Queueing Models

Qsim demonstrates the effects of arrival rates and service rates on queues.

runQsim S ST L AT T/F "Title" 

• S = Number of Servers
• ST = Average Service Time
• L = Queue Length
• AT = Average Interarrival Time
• T/F = true means single queue, false means multiple queues
• Title = the Title in quotes

Thank you!!

• Bob Allen - allen_r@mercer.edu
• Laurie White - white_la@mercer.edu
• You are welcome to play with our examples found in gw.zip