Oct 15, Fall 2009 IAT 800 1

IAT 800

ArrayList, Text, Java Libraries

Oct 15, Fall 2009 IAT 800 2

Topics

ArrayLists– ArrayLists + Polygons

Some words on Strings

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ArrayLists

Pros:– Are great if you don’t know how many things

are going to go into the array. – Automatically resizes when you add to a full

ArrayList. Cons:

– Only stores objects, not primitive variables (int, float…). Need to make objects from those.

– Only returns things of the Object type. Need to explicitly cast back to the type you put in there.

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ArrayLists

Remember, an ArrayList is just like an array:

If we decide we need to add another element to the array, we need to make a NEW, bigger array, and copy all the elements into it.

What a pain!

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ArrayLists

ArrayLists do this for us! We don’t even have to declare a size when we first create it, only deciding how many elements we’ll have when we actually add them.– ArrayList a = new ArrayList();– a.add(Object o) – adds an object at next index. – a.get(int i) – returns object at i index.– a.size() – returns number of items in the

ArrayList.

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Simple Example - ArrayList

Let’s make a little class called Point, which simply stores an X and Y value associated with a point on the screen.

class Point { int x, y; Point(int x, int y) { this.x = x; this.y = y; }}

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Simple Example - ArrayList

ArrayList of Points instead of two arrays of x and y points.

ArrayList pointList = new ArrayList();pointList.add(new Point(45, 50));pointList.add(new Point(79, 23));

// let’s draw a circle at our second point.Point p2 = (Point)pointList.get(1);ellipse(p2.x, p2.y, 50, 50);

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Simple Example - ArrayList

We could extend this so that every time we click, that point gets added to our ArrayList.

void mouseReleased() { pointList.add(new Point(mouseX, mouseY));}

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Simple Example - ArrayList

We could then do anything with these points as they accumulate. Here’s an example:

void draw() { background(255); if(pointList.size() > 1) { beginShape(); for(int i = 0; i < pointList.size(); i++) { Point p1 = (Point)pointList.get(i); vertex(p1.x, p1.y); } endShape(CLOSE); }}

Every time we click, thepolygon will re-draw, usingthe new point we’ve added.

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Types

You may recall when we talked about types– Primitives

• int, float, byte• boolean• char

– Objects (composites)• Array• ArrayList• PImage• (any object you create)• Strings

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String details

A string is almost like an array of chars– char someletter = 'b';– String somewords = "Howdy-do, mr. jones?";– Note the use of double-quotes (vs. apostrophes)

Like the objects we've created with classes, it has several methods, too…

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String methods

From http://processing.org/reference/String.html

– length() • returns the size of the String (number of letters)

– charAt(number) • returns the char at an index number

– toUpperCase() and toLowerCase()• returns a copy of the String in UPPERCASE or lowercase

respectively.

– substring(beginIndex, endIndex)• returns a portion of the String from beginIndex to

endIndex-1String howdy = "Hello!"; String expletive = howdy.substring(0,4);

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String concatenation

Concatenation is just a fancy word for slapping together to make one!

With Strings, this is done using the + symbol So, if you have:

You'll get out:

String s1 = "She is the "; String s2 = "programmer.“ ;

String sentence = s1 + "awesomest " + s2;

println(sentence); // sentence == "She is the awesomest programmer."

// outputs: She is the awesomest programmer.

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MORE String concatenation You can also add in numbers, too!

There is also a function called nf() which can format your numbers (it stands for number format)

It has siblings! nfs(); nfp(); nfc(); Consult the reference.

String anothersentence = s1 + "#"+ 2 + " " + s2;// "She is the #2 programmer."

anothersentence = s1 + nf(7,3) + " " + s2;// nf( integer, number of digits )// "She is the 007 programmer."

anothersentence = s1 + nf(3.14159,3,2) + " " + s2;// nf( float, digits before decimal, digits after decimal )// "She is the 003.14 programmer."

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Strings and Arrays

Did you know that you can take an Array of Strings and join it into one String?

Did you also know that you can split a String into an Array?

String[] a = { "One", "string", "to", "rule", "them", "all…" };

String tolkien = join(a, " ");// tolkien == "One string to rule them all…"

String b = "Another string to bind them…“ ;

String[] tolkien2= split(b, " ");// tolkien2 == { "Another", "string", "to", "bind", "them…" }

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Special characters

Split based on spaces (" ")– tab: "\t"– new line: "\n"

– other escape characters include "\\" "\""

String twolines = "I am on one line.String twolines = "I am on one line.\n\n I am I am \t\ton another."on another."

I am on one line.I am on one line.I am on I am on another.another.

( \ tells the computer to look to ( \ tells the computer to look to the next character to figure out the next character to figure out what to do that's special.)what to do that's special.)

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We started with Processing in…

// any code here, no methods

line(0,0,20,20);// methods!

// global varsint a;

// methodsvoid setup(){

}

void draw(){

}

// …with classes

// (all of the above and then)class Emotion {

//fields

//constructor

//methods

}

// …and subclasses!

// (ALL of the above, and…)

class Happy extends Emotion {

//new fields

//constructor

//methods

}

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Processing is actually a Java Class

// Java-Mode!!!

class Uneasy extends PApplet {

// void setup() and void draw() as normally …

//methods

//classes and subclasses

}

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Java Mode

Allows you to program in pure Java– Can import classes that aren’t normally imported into a

Processing app– Importing means making a classes available to your

program – the Java API docs tell you where classes are In Java mode, create a class that extends

PApplet– Normally, all Processing applets extend PApplet behind the

scenes

setup(), draw(), etc. are methods of the class extending PApplet

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A Java-mode programclass MyProgram extends PApplet {

void setup() { … }void draw() { … }

void myTopLevelMethod() { … }

class Text { // Text is just an example int xPos, yPos;String word;…

}}

Notice that any classes you define are inside the top class

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Why use Java-mode? Java-mode gives you access to the entire Java

SDK– We need access to some SDK classes for HTML parsing

that Processing doesn’t make visible by default

Java-mode helps you to understand how Processing is built on-top of Java– All those “magic” functions and variables are just

methods and fields of PApplet that your program inherits

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Libraries!

Libraries are other classes (in .java or .jar files )– Use import nameoflibrary.nameofmethod;

(e.g., import video.*; ) Now with Java-mode, you can ALSO put your

programs in multiple files– A file for each class– Create new tabs (files) with that button in the

upper right

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Recap

Strings Methods and

concatenation Strings and Arrays