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IAT 800

IAT 800. ArrayList, Text, Java Libraries. Topics. ArrayLists ArrayLists + Polygons Some words on Strings. 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:

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IAT 800

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  1. IAT 800 ArrayList, Text, Java Libraries IAT 800

  2. Topics • ArrayLists • ArrayLists + Polygons • Some words on Strings IAT 800

  3. 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. IAT 800

  4. 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! IAT 800

  5. 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. IAT 800

  6. 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; } } IAT 800

  7. 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); IAT 800

  8. 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)); } IAT 800

  9. 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, the polygon will re-draw, using the new point we’ve added. IAT 800

  10. 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 IAT 800

  11. 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… IAT 800

  12. 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-1 String howdy = "Hello!"; String expletive = howdy.substring(0,4); IAT 800

  13. 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. IAT 800

  14. 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." IAT 800

  15. 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…" } IAT 800

  16. Special characters • Split based on spaces (" ") • tab: "\t" • new line: "\n" • other escape characters include"\\" "\"" ( \ tells the computer to look to the next character to figure out what to do that's special.) String twolines = "I am on one line.\n I am \ton another."I am on one line.I am on another. IAT 800

  17. 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 } IAT 800

  18. Processing is actually a Java Class // Java-Mode!!! class Uneasy extends PApplet { // void setup() and void draw() as normally … //methods //classes and subclasses } IAT 800

  19. 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 IAT 800

  20. A Java-mode program class 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 IAT 800

  21. 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 IAT 800

  22. 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 IAT 800

  23. Recap • Strings • Methods and concatenation • Strings and Arrays IAT 800

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