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GridWorldAn Introduction

Frances P. Trees, Drew UniversityBarbara Ericson, Georgia Tech____________________________Donald Allen, Troy High SchoolAnn Shen, Bishop Strachan SchoolLaurie White, Mercer University

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Why Use Case Studies?

Allow students the benefits of apprenticeship. Make large programs accessible to students. Particularly well suited for active learning and team work. Encourage students to reflect on solutions. The least gender-biased of all types of AP Free Response questions.

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AP Overview Framework derived from MBS (GNU license!)Fewer classes/interfaces: 4 (A) / 7 (AB) implementations, 5 API'sLayers: use framework at multiple points in your courseMuch easier to add your own classes

public classes

A AAPI API

API

API API

AB

AB AB

BoxBug ChameleonCritterA A

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OverviewLayers of Information

Layer 1: ObjectsLayer 2: Simple InheritanceLayer 3: Interacting ObjectsLayer 4: Data Structures

Narrative (Student Manual) Part 1: Provides experiments to observe the attributes and behavior of the actors.Part 2: Defines Bug variations.Part 3: Explores the code that is needed to understand and create actors.Part 4: Defines classes that extend the Critter class.Part 5: (CS AB only) Explains grid data structures.

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Layer 1: Objects Turtle-like graphics: Bugdrops flowers

Direct Manipulation (like in BlueJ)

Can be used as an early introduction to objects

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GridWorldPart 2

Bug Variations

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Layer 2: Simple InheritancePart 2: Bug Variations

Simple Inheritance

Demo:BoxBug (testable code)BoxBugRunner

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BoxBug

Students need to understandBug constructorsAct method

Students will need to usecanMoveturnmove

Students can create a new type of Bug by modifying BoxBug code

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Extending the Bug class

Override Bug's act method

Each call to the move method should be guarded by a call to the canMove method

Add additional instance fields if needed

Add new methods to the subclass if needed

Constructors for the subclass call super() or super(someColor)

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New Bug Classes

CircleBugLike BoxBug but only one turn

45 degree turn

SpiralBugLike BoxBug but the sideLength gets longer after each turn

90 degree turn

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New Bug Classes

ZBugDraws a Z and then stops moving

DancingBugTakes an array of integers which are the number of turns it makes when asked to actThen it acts like a Bug

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Some easy, student-designed bugs…

MirrorBugThis bug, when turning, would turn left instead of right.

BoostBugThis bug works like a power-up in a video game. If a bug moves to a location containing a flower, it eats that flower and it turns 2 times instead of once.

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Cool bugs!

Fruit Flies !!!

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GridWorldPart 3

Explore GridWorld Classes

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Part 3: GridWorld Classes and InterfacesA grid contains ActorsTwo types of grids

boundedunbounded

Locations in the grid are represented by objects of type LocationAn Actor knows what grid it lives in and its location within that grid.

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The Actor class

When adding or removing actors, do not use the put and remove methods of the Gridinterface.

Those methods do not update the location and grid instance variables of the actor. That is a problem since most actors behave incorrectly if they do not know their location. To ensure correct actor behavior, always use the putSelfInGridand removeSelfFromGrid methods of the Actorclass.

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The Actor class

The moveTo method allows the actor to move to any valid location. If the actor calls moveTofor a location that contains another actor, the other one removes itself from the grid and this actor moves into that location.

The act method of the Actor class reverses the direction of the actor. You override this method in subclasses of Actor to define actors with different behavior.

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Cool programs dealing with actors:

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GridWorldPart 4

The Critter class and Extensions

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Layer 3: Interacting Objects(Part 4)

Introduces the Critter class (testable code)Uses template method, actIt is usually not a good idea to override the act method in a Critter

subclass. The Critter class was designed to represent actors that process other actors and then move. If you find the act method unsuitable for your actors, you should consider extending Actor, not Critter.

The act method calls five methods accomplishing the following tasks:

find neighbors (getActors)process neighbors (processActors)find candidates for move locations (getMoveLocations)select a move location (selectMoveLocation)make a move (makeMove)

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Critters

Get all neighborsat 8 surrounding locations

Eat neighbors that are not rocks and not critters

at 8 surrounding locationsCan move to any empty adjacent location

picked at randomMoves to the new location

doesn't turn

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ChameleonCritter (testable code)

ChameleonCritteroverrides processActors and makeMove.

Randomly selects a neighbor and changes this critter's color to be the same as that neighbor's. If there are no neighbors, no action is taken.Turns towards the new location as it moves

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CrabCritter

CrabCritter overrides getActors, getMoveLocations, and makeMove.

A crab gets the actors in the three locations immediately in front, to its front-right and to its front-leftpossible move locations are immediately to the right and to the leftIf the crab critter doesn't move, it randomly turns left or right

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Creative Critters…

A ChameleonKid changes its color to the color of one of the actors immediately in front or behind. If there is no actor in either of these locations, then the ChameleonKid darkens like the modified ChameleonCritter.

A RockHound gets the actors to be processed in the same way as a Critter. It removes any rocks in that list from the grid. A RockHound moves like a Critter.

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Creative Critters…

Create a class KingCrab that extends CrabCritter. A KingCrab gets the actors to be processed in the same way a CrabCritter does. A KingCrab causes each actor that it processes to move one location further away from the KingCrab. If the actor cannot move away, the KingCrab removes it from the grid. When the KingCrab has completed processing the actors, it moves like a CrabCritter.

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Fun Critters

FruitCritters

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Overview of GridWorld Creatures

ActorsBugs

extending Bug: override ActRocksFlowersCritters

DO NOT OVERRIDE ACT!!!extending Critter overrides one or more of the 5 methods

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Don't like bugs and critters????

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GridWorldLayer 5

Data Structures – AB only

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Layer 4: Data Structures (Part 5) AB onlyGrid Data StructuresTwo concrete implementations of the Grid interface are provided,

one for a bounded grid that has a fixed number of rows and columnsone for an unbounded grid, for which any row and column values are valid.

Rather than have repeated code in two classes, the AbstractGrid class defines five methods of the Grid interface that are common to both implementations.

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Grid Hierarchy

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Extentions…

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Mice in a MazeAdded a Wall, Mouse, and Smart Mouse

inherit from ActorAdded WallDisplay, MouseDisplay, and SmartMouseDisplay

inherit from AbstractDisplayThe mice are trying to get to the cheese

exit when find cheeseCan add stacks and queues for "smarter" mice

depth-first searchbreadth-first search

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School Time…………

School busses must be able to collect students form the bus stops, bring them to schools, and return them to the correct bus stop at the end of the day.

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An Extension - GameOfLife

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An Extension - Sudoku

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Extensions – Tile Gameshttp://www.apcomputerscience.com/gridworld/

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Beyond GridWorldGreenfoot is a free Java framework www.greenfoot.orgYou can do GridWorldin GreenfootYou can also move beyond fitting everything in the grid

do games like Breakout

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Available GridWorld Materials

Code (.zip/238KB)

Student Manual (Narrative and Appendixes as a Single Document)Student Manual (.pdf/633KB)

Narrative as individual files:Part 1: Observing and Experimenting with GridWorld (.pdf/211KB)Part 2: Bug Variations (.pdf/285KB)Part 3: GridWorld Classes and Interfaces (.pdf/156KB)Part 4: Interacting Objects (.pdf/224KB)Part 5: Grid Data Structures (CS AB only) (.pdf/150KB)

Support material for GridWorldInstallation Guide (.pdf/172KB)Appendixes (Quick Reference document) (145KB)Solutions Manual (.pdf/374KB)

GridWorld Sample Exam QuestionsGridWorld Sample Questions (.pdf/238KB) New!XBug Sample Code (.zip/3KB) New!Drop Game Sample Code (.zip/3KB) New!

http://apcentral.collegeboard.com/apc/public/courses/teachers_corner/151155.html

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What's tested?

AP Quick Reference Guide Appendix A includes a table with this informationhttp://apcentral.collegeboard.com/apc/members/repos

itory/ap07_gridworld_quickref_v2.pdf;jsessionid=G1QQPDMPd0pYfMyV9xYMJfSgQhTY475Zyp2GydkN33Y1F5zB54Ms!-28784328

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Helpful/Interesting URLs

http://www.apcomputerscience.com/gridworld/Dave Wittry's Board GamesReg Hahne's Save A Heart(apteacher,specialfocus)

http://www.apluscompsci.com/gridworld.htmTreeBoundedGrid, Othello, Sudoku, AntFarmRobert Glenn Martin's GridWorld materials (abbott)

http://www.cs.sbu.edu/dlevine/RolePlay/roleplay.html

Dave Levine's Role Play

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Helpful/Interesting URLshttp://horstmann.com/gridworld/

http://horstmann.com/gridworld/api-notes.htmlCay Horstmann's GridWorld site

http://csta.villanova.edu/http://www.dare.k12.nc.us/langner/gridworld/FreeResponseRewritten4Gridworld.doc

free response questions rewritten in GridWorldhttp://www.dare.k12.nc.us/langner/gridworld/GridWorldFRSolutions.doc - solutions

http://www.greenfoot.org/Place to download Greenfoot

http://csta.acm.org/index.htmlCSTA : Join and download and contribute resources here