Georgia Institute of Technology

Simulations

Barb Ericson

ericson@cc.gatech.edu

Jan 2005

Georgia Institute of Technology

Learning Goals

• Understand that object-oriented programs are simulations– of turtles– of robots– of card games– of fish

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Computers as Simulators

• “The computer is the Proteus of machines. Its essence is its universality, its power to simulate. Because it can take on a thousand forms and serve a thousand functions, it can appeal to a thousand tastes.” Seymour Papert in Mindstorms

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History of Turtles

• Seymour Papert at MIT in the 60s– By teaching the computer to do something the

kids are thinking about thinking• Develop problem solving skills• Learn by constructing and debugging something

– Learn by making mistakes and fixing them

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Using Turtles

• Classes created at Georgia Tech– As part of a undergraduate class

• Add bookClassesFinal to your classpath

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Turtle Basics

• The turtle starts off facing north and in the center of the world by default– World world1 = new

World();– Turtle turtle1 = new

Turtle(world1);

• Turtles can move forward – turtle1.forward(100);

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Turning a Turtle

• Turtles can turn– Positive turns to right

• turtle1.turn(90);• turtle1.forward(100);

– Negative turns to the left

• turtle1.turn(-90);• turtle1.forward(50);

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The Pen

• Each turtle has a pen– The default is to have

the pen down to leave a trail

– You can pick it up:• turtle1.penUp();• turtle1.turn(-90);• turtle1.forward(70);

– You can put it down again:

• turtle1.penDown();• turtle1.forward(100);

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More Turtle Behaviors

• Turtles can move to a specific location– turtle1.moveTo(400,10);

• Of course, you can create many turtles and move them all– Run TurtleTest

• Creates 1000 turtles and puts them in an array of turtles. Has each turn by a random amount from 0 to 359 and go forward by 100

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Objects can Refuse

• Turtles won’t move completely out of the boundaries of the world– World world2 = new

World();– Turtle turtle2 = new

Turtle(world2);– turtle2.forward(600);

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Objects send Messages

• Objects don’t “tell” each other what to do– They “ask” each other to do things

• Ask don’t tell

• Objects can refuse to do what they are asked– The object must protect it’s data

• Not let it get into an incorrect state

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Challenge

• Write a method to have a turtle draw some basic shapes– Square– Triangle– Hexagon– Circle– Spiral

• Use these methods to draw a simple house

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Karel J. Robot

• Set of classes developed to teach object-oriented programming

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Using Karel J. Robot• Karel code is in karelpremeir0407

– I modified the directories to match the package name– I also modified the constructor to be public

• Follow the on-line book at http://csis.pace.edu/~bergin/KarelJava2ed/ch1/index.html

• Add KarelJRobot.jar to the classpath. You may need to add the directory karelpremeir0407 as well.

• Edit KarelMain.java to try things out– World.setVisible(true); // not visible to start– World.readWorld(String file) // reads the file– UrRobot karel = new UrRobot(1, 1, East, 0, Color.red); // create a

robot at 1,1 facing east with 0 beepers and a red badge

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Robot Behaviors

• move() // moves 1 block

• turnLeft() // turns 90 degrees left

• pickBeeper() // picks up a beeper

• putBeeper() // drops a beeper

• userPause(String message) // wait for user

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World Builder

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Using the World Builder

• Double click on KarelJRobot.jar to bring up the world builder

• Use it to position walls and beepers

• Save it to a file

• Modify KarelMain to read that file

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Robot Challenges

• Create a maze of walls and write a method to get the robot through the maze

• Have the robot create a pattern by dropping beepers (like a pyramid)

• Have several robots work together to gather beepers

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Card Games

• There are public domain card images available at – http://www.waste.org/~oxymoron/files/cards

• Dr. Estell of Ohio Northern University has some card game projects at http://nifty.stanford.edu/2004/EstellCardGame/index.html – CardAssingment.doc

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Fish

• Alyce Brady of Kalamazoo College – Page of resources

• http://max.cs.kzoo.edu/AP/MBS/index.html

– Aquarium Lab Series• Review of basics and set-up for Marine Biology

Case Study– http://max.cs.kzoo.edu/patterns/JavaPatternLabs/

AquariumLabSeries/index.shtml

– Minnow Project• http://max.cs.kzoo.edu/AP/MBS/

RelatedAssignments/Minnow/MinnowProj.html

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Summary• Object-oriented programs are simulations

– Consist of interacting objects who send each other messages

• Objects can refuse to do what you ask

• Objects belong to classes– An object is an instance of a class– Classes describe the data and operations that all

objects of the class will have – A class creates objects

• Objects are responsible – They should control their data– They each have their own copy of their data