l 5 Java Turtles

7/30/2019 l 5 Java Turtles

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CS 141 Turtles!

CS 141 Introduction to Computer Science

Its Turtles all the way down...

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1Sunday, September 16, 2012


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CS 141 Turtles! 2

References

(some slides taken from lectures provided by Barbara

Ericson, Georgia Tech for her Multimedia Computationcourse)



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Intro to JavaCS 141

ARRRR!!!!!

Its Talk Like a Pirate Day!

http://www.talklikeapirate.com/howto.html

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http://www.talklikeapirate.com/howto.htmlhttp://www.talklikeapirate.com/howto.htmlhttp://www.talklikeapirate.com/howto.html


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CS 141 Turtles! 4

Computers as Simulators

The computer is the Proteus of machines. Its essence

is its universality, its power to simulate. Because it cantake on a thousand forms and serve a thousand

functions, it can appeal to a thousand tastes.

Seymour Papert in Mindstorms

He can foretell the future, but, in a mytheme familiar

from several cultures, will change his shape to avoid

having to; he will answer only to someone who is

capable of capturing him. From this feature of Proteuscomes the adjectiveprotean, with the general meaning

of "versatile", "mutable", "capable of assuming many

forms". "Protean" has positive connotations of

flexibility, versatility and adaptability. (Wikipedia)

http://en.wikipedia.org/wiki/Adjectivehttp://en.wikipedia.org/wiki/Adjectivehttp://en.wikipedia.org/wiki/Mythemehttp://en.wikipedia.org/wiki/Mytheme


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Creating a Simulation

Computers let us simulate things

We do this by creating models of the things we wantto simulate

We need to define what types of objects we will wantin our simulation and what they can do

Classes define the types and create objects of that type

Objects act in the simulation



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CS 141 Turtles! 6

Turtles!

Well simulate a world populated with turtles

carrying pens

We have to define what we mean by a Turtle to thecomputer

We compile it to convert it into something the

computer can understand



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CS 141 Turtles! 7

History of Turtles

Seymour Papert at MIT in the 60s

By teaching the computer to do something the kids arethinking about thinking Develop problem solving skills

Learn by constructing and debugging something

Learn by making mistakes and fixing them



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CS 141 Turtles! 8

Creating Objects in Java

In Java to create an object of a class you use

new (value, value, );

Our Turtle objects live in a World object

new World();



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CS 141 Turtles! 9

Naming is Important

If you get a new pet one of the first things you do is

name it

In programming we name things we want to refer to

again

Gives us a way to work with them



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CS 141 Turtles! 10

Saving a Reference to an Object

To be able to refer to an object again we need to

specify what type of thing it is and give it a name

This is also called declaring a variable

Class name; OR

Class name = new Class(value, value, );

The equal sign assigns the value of the variable on theleft to the result of the stuff on the right



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CS 141 Turtles! 11

Turtle Basics

The world starts off with a size of 640 by 480 with no

turtles

World w = new World();

The turtle starts off facing north and in the center ofthe world by default

You must pass a World object when you create the

Turtle object or you will get an error:java.lang.NoSuchMethodException

Turtle ted = new Turtle(w);



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CS 141 Turtles!

Turtle moves

turtle.forward(steps);

turtle.backward(steps);

turtle.turnRight();

turtle.turnLeft();

turtle.turn(degrees);

turtle.penUp();

turtle.penDown();

turtle.moveTo(x, y); (0,0) is at the upper left.

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CS 141 Turtles!

turtle.penWidth(size);

turtle.setPenColor(Color); // must import java.awt.Color;

turtle.setColor(Color);

turtle.setBodyColor(Color);

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CS 141 Turtles! 14

Objects send Messages

Objects dont tell each other what to do

They ask each other to do things

Objects can refuse to do what they are asked

The object must protect its data Not let it get into an incorrect state

A bank account object shouldnt let you withdraw more

money that you have in the account


C i M h d


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Creating a Method

The syntax for declaring a method is

visibility returnType name(parameterList)

Visibility determines access

The returnType is the type of thing returned

Name the method starting with a lowercase word and uppercasing

the first letter of each additional word (CamelCase)



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CS 141 Turtles!

Drawing Polygons

rectangle - easy

equilateral triangle?

pentagon?

hexagon?

a general formula for a regular polygon?

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Circles?

How to draw a circle with a Turtle?

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Ch ll (T th t h )


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Challenges (Try these at home)

Create a method for drawing an equilateral triangle

all sides have the same length

Pass in the length

Create a method for drawing a diamond

Create a method for drawing a house

Using the other methods


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