GridWorld
An Introduction
Frances P. Trees, Drew University
Barbara Ericson, Georgia Tech
____________________________
Donald Allen, Troy High School
Ann Shen, Bishop Strachan School
Laurie White, Mercer University
CS&IT 2008
1
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.
CS&IT 2008
2
AP Overview
ƒ
ƒ
ƒ
ƒ
Framework derived from MBS (GNU license!)
Fewer classes/interfaces: 4 (A) / 7 (AB) implementations, 5 API's
Layers: use framework at multiple points in your course
Much easier to add your own classes
API
public
classes
API
API
API
AB
API
A
AB
A
AB
ChameleonCritter
BoxBug
A
A
CS&IT 2008
3
Overview
ƒ Layers of Information
ƒ
ƒ
ƒ
ƒ
Layer 1: Objects
Layer 2: Simple Inheritance
Layer 3: Interacting Objects
Layer 4: Data Structures
ƒ Narrative (Student Manual)
ƒ Part 1: Provides experiments to observe the attributes
and behavior of the actors.
ƒ Part 2: Defines Bug variations.
ƒ Part 3: Explores the code that is needed to understand
and create actors.
ƒ Part 4: Defines classes that extend the Critter class.
ƒ Part 5: (CS AB only) Explains grid data structures.
CS&IT 2008
4
Layer 1: Objects
Can be used as an early introduction to objects
ƒ Turtle-like graphics: Bug
drops flowers
ƒ Direct Manipulation
(like in BlueJ)
CS&IT 2008
5
GridWorld
Part 2
Bug Variations
CS&IT 2008
6
Layer 2: Simple Inheritance
Part 2: Bug Variations
ƒ Simple Inheritance
ƒ Demo:
ƒ BoxBug (testable code)
ƒ BoxBugRunner
CS&IT 2008
7
BoxBug
„
„
Students need to understand
‰
Bug constructors
‰
Act method
Students will need to use
‰
‰
‰
‰
canMove
turn
move
Students can create a new type of Bug by modifying
BoxBug code
CS&IT 2008
8
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)
CS&IT 2008
9
New Bug Classes
„
CircleBug
‰
Like BoxBug but only one
turn
„
„
45 degree turn
SpiralBug
‰
Like BoxBug but the
sideLength gets longer
after each turn
„
90 degree turn
CS&IT 2008
10
New Bug Classes
„
ZBug
‰
„
Draws a Z and then
stops moving
DancingBug
‰
‰
Takes an array of
integers which are the
number of turns it makes
when asked to act
Then it acts like a Bug
CS&IT 2008
11
Some easy, student-designed bugs…
„
MirrorBug
‰
„
This bug, when turning, would turn left instead of
right.
BoostBug
‰
This 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.
CS&IT 2008
12
Cool bugs!
„
Fruit Flies !!!
CS&IT 2008
13
GridWorld
Part 3
Explore GridWorld Classes
CS&IT 2008
14
Part 3: GridWorld Classes and Interfaces
„
„
A grid contains Actors
Two types of grids
‰
‰
„
„
bounded
unbounded
Locations in the grid are represented by objects of type Location
An Actor knows what grid it lives in and its location within that grid.
CS&IT 2008
15
The Actor class
„
When adding or removing actors, do not use
the put and remove methods of the Grid
interface.
‰
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 putSelfInGrid
and removeSelfFromGrid methods of the Actor
class.
CS&IT 2008
16
The Actor class
„
The moveTo method allows the actor to move
to any valid location. If the actor calls moveTo
for 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.
CS&IT 2008
17
Cool programs dealing with actors:
CS&IT 2008
18
GridWorld
Part 4
The Critter class and Extensions
CS&IT 2008
19
Layer 3: Interacting Objects
(Part 4)
ƒ Introduces the Critter class (testable code)
ƒ Uses template method, act
It 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.
ƒ The act method calls five methods accomplishing the following
tasks:
ƒ find neighbors (getActors)
ƒ process neighbors (processActors)
ƒ find candidates for move locations (getMoveLocations)
ƒ select a move location (selectMoveLocation)
ƒ make a move (makeMove)
CS&IT 2008
20
Critters
„
Get all neighbors
‰
„
Eat neighbors that are not
rocks and not critters
‰
„
at 8 surrounding locations
Can move to any empty
adjacent location
‰
„
at 8 surrounding locations
picked at random
Moves to the new location
‰
doesn't turn
CS&IT 2008
21
ChameleonCritter (testable code)
„
ChameleonCritter
overrides
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
CS&IT 2008
22
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-left
possible move locations are
immediately to the right and
to the left
If the crab critter doesn't
move, it randomly turns left
or right
CS&IT 2008
23
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.
CS&IT 2008
24
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.
CS&IT 2008
25
Fun Critters
„
CS&IT 2008
FruitCritters
26
Overview of GridWorld Creatures
„
Actors
‰
Bugs
„
‰
‰
‰
extending Bug: override Act
Rocks
Flowers
Critters
„
„
DO NOT OVERRIDE ACT!!!
extending Critter overrides one or more of the 5
methods
CS&IT 2008
27
Don't like bugs and critters????
CS&IT 2008
28
GridWorld
Layer 5
Data Structures – AB only
CS&IT 2008
29
Layer 4: Data Structures (Part 5) AB only
„
„
Grid Data Structures
Two concrete implementations of the Grid
interface are provided,
‰
‰
„
one for a bounded grid that has a fixed number of
rows and columns
one 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.
CS&IT 2008
30
Grid Hierarchy
CS&IT 2008
31
Extentions…
CS&IT 2008
32
Mice in a Maze
„
Added a Wall, Mouse, and
Smart Mouse
‰
„
Added WallDisplay,
MouseDisplay, and
SmartMouseDisplay
‰
„
inherit from AbstractDisplay
The mice are trying to get to
the cheese
‰
„
inherit from Actor
exit when find cheese
Can add stacks and queues
for "smarter" mice
‰
‰
depth-first search
breadth-first search
CS&IT 2008
33
School Time…………
„
CS&IT 2008
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.
34
An Extension - GameOfLife
CS&IT 2008
35
An Extension - Sudoku
CS&IT 2008
36
Extensions – Tile Games
http://www.apcomputerscience.com/gridworld/
CS&IT 2008
37
Beyond GridWorld
„
„
„
Greenfoot is a free
Java framework
www.greenfoot.org
You can do GridWorld
in Greenfoot
You can also move
beyond fitting
everything in the grid
‰
do games like Breakout
CS&IT 2008
38
Available GridWorld Materials
http://apcentral.collegeboard.com/apc/public/courses/teachers_corner/151155.html
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 GridWorld
Installation Guide (.pdf/172KB)
Appendixes (Quick Reference document) (145KB)
Solutions Manual (.pdf/374KB)
GridWorld Sample Exam Questions
GridWorld Sample Questions (.pdf/238KB) New!
XBug Sample Code (.zip/3KB) New!
Drop Game Sample Code (.zip/3KB) New!
CS&IT 2008
39
What's tested?
„
AP Quick Reference Guide Appendix A
includes a table with this information
http://apcentral.collegeboard.com/apc/members/repos
itory/ap07_gridworld_quickref_v2.pdf;jsessionid=G1
QQPDMPd0pYfMyV9xYMJfSgQhTY475Zyp2Gydk
N33Y1F5zB54Ms!-28784328
CS&IT 2008
40
Helpful/Interesting URLs
„
http://www.apcomputerscience.com/gridworld/
‰
‰
„
http://www.apluscompsci.com/gridworld.htm
‰
‰
„
Dave Wittry's Board Games
Reg Hahne's Save A Heart
(apteacher,specialfocus)
TreeBoundedGrid, Othello, Sudoku, AntFarm
Robert Glenn Martin's GridWorld materials (abbott)
http://www.cs.sbu.edu/dlevine/RolePlay/rolepla
y.html
‰
Dave Levine's Role Play
CS&IT 2008
41
Helpful/Interesting URLs
„
http://horstmann.com/gridworld/
‰
‰
„
„
http://csta.villanova.edu/
http://www.dare.k12.nc.us/langner/gridworld/FreeRespon
seRewritten4Gridworld.doc
‰
‰
„
free response questions rewritten in GridWorld
http://www.dare.k12.nc.us/langner/gridworld/GridWorldFRSolutio
ns.doc - solutions
http://www.greenfoot.org/
‰
„
http://horstmann.com/gridworld/api-notes.html
Cay Horstmann's GridWorld site
Place to download Greenfoot
http://csta.acm.org/index.html
‰
CSTA : Join and download and contribute resources here
CS&IT 2008
42