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Using ArrayList in Java for Dynamic Array Management in a Drawing Tool Project, Study Guides, Projects, Research of Communication

Georgia Institute of Technology - Main Campus Communication

An overview of using arraylist in java for managing a dynamic number of asteroids in a drawing tool project. It covers the basics of arraylist, including its resizable nature, methods like add(), get(), remove(), and size(), and the need to cast back to the more detailed type when retrieving objects from the arraylist. The document also discusses the concept of super and this in java, and how they can be used in the context of the asteroid class. Finally, it explains how to create and initialize an arraylist, and how to use it to draw and destroy asteroids.

Typology: Study Guides, Projects, Research

Pre 2010

Uploaded on 08/05/2009

koofers-user-hfz 🇺🇸

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Don't miss anything!

LCC 6310

The Computer as an

Expressive Medium

Lecture 9

Overview

Programming questions related to project 2? (due Friday 6pm!)

Programming concepts

super and this

Java SDK classes

Lists

Reading the Java docs

Free time to work on project 2

Project 2

Create your own drawing tool, emphasizing algorithmic

generation/modification/manipulation. Explore the balance of control

between the tool and the person using the tool. The tool should do

something different when moving vs. dragging (moving with the

mouse button down). The code for your tool should use at least one

class.

Revisiting our example

So far we have a rocket that flies around in a field of asteroids and

fires missiles

Now we want our missiles to blow up asteroids

This means we need a variable number of asteroids

How do we do this with an array? (They have a fixed size)

We can use a special Java object called an ArrayList!

We'll also need to figure out when we have a collision

Discover Study Guides, Projects, Research of Communication Georgia Institute of Technology - Main Campus

Partial preview of the text

Download Using ArrayList in Java for Dynamic Array Management in a Drawing Tool Project and more Study Guides, Projects, Research Communication in PDF only on Docsity!

LCC 6310

The Computer as an

Expressive Medium

Lecture 9

Overview

Programming questions related to project 2? (due Friday 6pm!)Programming concepts

super and thisJava SDK classes

ListsReading the Java docs

Free time to work on project 2

Project 2

Create your own drawing tool, emphasizing algorithmicgeneration/modification/manipulation. Explore the balance of controlbetween the tool and the person using the tool. The tool should dosomething different when moving vs. dragging (moving with themouse button down). The code for your tool should use at least oneclass.

Revisiting our example

So far we have a rocket that flies around in a field of asteroids andfires missilesNow we want our missiles to blow up asteroids

This means we need a variable number of asteroidsHow do we do this with an array? (They have a fixed size)We can use a special Java object called an ArrayList!We'll also need to figure out when we have a collision

The Java SDK

(Java SDK = Java Software Developer's Kit)Java comes with thousands of classes in the Java Platform APIDocumentation is available on Sun’s website

http://java.sun.com/j2se/1.4.2/docs/api/index.htmlNote that Processing supports Java 1.4.2 features (not yet 1.5)You may want to download the documentation…

Let’s look at ArrayList

ArrayList

ArrayList is a resizeable list

This means we can add and delete things from the list without worryingabout declaring the size up front

The main methods we care about are add(), get(), remove(), and size()

http://java.sun.com/j2se/1.4.2/docs/api/index.html

Steps for using ArrayList

Declare a variable of type ArrayListCreate a new ArrayList and assign it to the variableCall add(), get(), remove() and size() on the ArrayList as you need them

Parents and children

Remember that we declared a child class ArmedRocket whose parentwas Rocket, and remember that classes are types

So ArmedRocket is a type and Rocket is a type

So, here are some legal assignments:

ArmedRocket

r1 = new

ArmedRocket(50, 60, 0);

Rocket

r2 =

new Rocket(50,

Rocket

r3 =

new ArmedRocket(50, 60, 0);

But this one is illegal:

ArmedRocket

r4 = new

Rocket(50, 60, 0);

Same goes for method arguments as well…

Using ArrayList.add()

The argument type of the add method is Object

Object is the parent class of all classesWith an object argument type, you can pass in an object of any class

So, let's declare our asteroids ArrayList…

ArrayList

asteroids;

And then initialize our asteroids…

asteroids

new

ArrayList();

for

(int i

i

NUM_ASTEROIDS;

i++)

asteroids.add(new

Asteroid());

Let's try this in Processing…

Destroying asteroids

When a missile hits an Asteroid, we need to destroy it

This was the whole reason for using ArrayList!Big asteroids turn into two small asteroidsSmall asteroids disappear void destroy(ArrayList asteroids) {

asteroids.remove(this);if (large) {

asteroids.add(new Asteroid(false, xPos, yPos, lastDrawMillis));asteroids.add(new Asteroid(false, xPos, yPos, lastDrawMillis));

Hmm… we've added some new things here:

We need to store the size of the Asteroid (is it large or small?)We need to be able to create new smaller Asteroids at a specifiedposition

Asteroid size

Since we only want two sizes (big and small) we can use a boolean:

boolean

large;

We also need to put something in the Asteroid's drawMe() method tomake sure that it will get drawn at the right size

Let's make small Asteroids at half-scale if (!large)

scale(0.5);

Now let's think about how to create the new smaller Asteroids at agiven (x,y) position…

super and this

this is a special variable keyword that always refers to the currentinstance (object)

Useful in methods to refer to yourselfthis.method() – calls a method on yourself (but normally you justdirectly call the method)this() – calls a constructor on yourself (useful for one version of aconstructor to call another)this.someVariable – refers to the class variable (useful if a variable oflocal scope has the same name as some class variable)

super is a special variable that always refers to the superclass portionof an object (the object cast into it’s superclass)

super.method() – calls a method on the superclasssuper() – calls a constructor on the superclass

A new Asteroid constructor

Asteroid(boolean

isLarge,

float

initialX,

float

initialY,

long

previousDrawTime)

{

set

the

initial

and

pos

xPos

initialX;

yPos

initialY;

get

random

orientation

for

this

asteroid

rotation

random(0,

TWO_PI);

get

the

asteroid's

velocity

and

directions

based

its

orientation

and

size

(bigger

moves

slower)

(isLarge)

{

velocityX

sin(rotation)*10;

velocityY

-cos(rotation)*10;

}

else

{

velocityX

sin(rotation)*25;

velocityY

-cos(rotation)*25;

} large

isLarge;

lastDrawMillis

previousDrawTime;

}

But what about the old constructor?

We still want to be able to create an Asteroid in a random location

So we want to keep our original constructor without parameters, but weneed to update it to take into account the asteroid size (they start big)We can just use this to call our new constructor and let it do all the work Asteroid() {

// create an asteroid at a random location on the displaythis (true, random(0, XSIZE), random(0, YSIZE), 0);

Let's assemble all these Asteroid changes together and put them inProcessing…

The size variable…

Storing our size

boolean

large;

Drawing at the correct size

after translating

and

rotating,

we

should

make

sure

to

scale

ourselves too

if

(!large)

scale(0.5);

The constructors…

Asteroid()

{

this

(true,

random(0,

XSIZE),

random(0,

YSIZE),

0);

} Asteroid(boolean

isLarge,

float

initialX,

float

initialY,

long

previousDrawTime)

{

xPos

initialX;

yPos

initialY;

rotation

random(0,

TWO_PI);

(isLarge)

{

velocityX

sin(rotation)*10;

velocityY

-cos(rotation)*10;

}

else

{

velocityX

sin(rotation)*25;

velocityY

-cos(rotation)*25;

} large

isLarge;

lastDrawMillis

previousDrawTime;

}

Using ArrayList in Java for Dynamic Array Management in a Drawing Tool Project, Study Guides, Projects, Research of Communication

Related documents

Partial preview of the text

Download Using ArrayList in Java for Dynamic Array Management in a Drawing Tool Project and more Study Guides, Projects, Research Communication in PDF only on Docsity!

LCC 6310

The Computer as an

Expressive Medium

Lecture 9

Overview

Programming questions related to project 2? (due Friday 6pm!)Programming concepts

super and thisJava SDK classes

ListsReading the Java docs

Free time to work on project 2

Project 2

Revisiting our example

So far we have a rocket that flies around in a field of asteroids andfires missilesNow we want our missiles to blow up asteroids

This means we need a variable number of asteroidsHow do we do this with an array? (They have a fixed size)We can use a special Java object called an ArrayList!We'll also need to figure out when we have a collision

The Java SDK

(Java SDK = Java Software Developer's Kit)Java comes with thousands of classes in the Java Platform APIDocumentation is available on Sun’s website

http://java.sun.com/j2se/1.4.2/docs/api/index.htmlNote that Processing supports Java 1.4.2 features (not yet 1.5)You may want to download the documentation…

Let’s look at ArrayList

ArrayList

ArrayList is a resizeable list

This means we can add and delete things from the list without worryingabout declaring the size up front

The main methods we care about are add(), get(), remove(), and size()

http://java.sun.com/j2se/1.4.2/docs/api/index.html

Steps for using ArrayList

Declare a variable of type ArrayListCreate a new ArrayList and assign it to the variableCall add(), get(), remove() and size() on the ArrayList as you need them

Parents and children

Remember that we declared a child class ArmedRocket whose parentwas Rocket, and remember that classes are types

So ArmedRocket is a type and Rocket is a type

So, here are some legal assignments:

ArmedRocket

r1 = new

ArmedRocket(50, 60, 0);

Rocket

r2 =

new Rocket(50,

Rocket

r3 =

new ArmedRocket(50, 60, 0);

But this one is illegal:

ArmedRocket

r4 = new

Rocket(50, 60, 0);

Same goes for method arguments as well…

Using ArrayList.add()

The argument type of the add method is Object

Object is the parent class of all classesWith an object argument type, you can pass in an object of any class

So, let's declare our asteroids ArrayList…

ArrayList

asteroids;

And then initialize our asteroids…

asteroids

new

ArrayList();

for

(int i

i

NUM_ASTEROIDS;

i++)

asteroids.add(new

Asteroid());

Let's try this in Processing…

Destroying asteroids

When a missile hits an Asteroid, we need to destroy it

This was the whole reason for using ArrayList!Big asteroids turn into two small asteroidsSmall asteroids disappear void destroy(ArrayList asteroids) {

asteroids.remove(this);if (large) {

asteroids.add(new Asteroid(false, xPos, yPos, lastDrawMillis));asteroids.add(new Asteroid(false, xPos, yPos, lastDrawMillis));

Hmm… we've added some new things here:

We need to store the size of the Asteroid (is it large or small?)We need to be able to create new smaller Asteroids at a specifiedposition

Asteroid size

Since we only want two sizes (big and small) we can use a boolean:

boolean

large;

We also need to put something in the Asteroid's drawMe() method tomake sure that it will get drawn at the right size

Let's make small Asteroids at half-scale if (!large)

scale(0.5);

Now let's think about how to create the new smaller Asteroids at agiven (x,y) position…

super and this