Sep 26, Fall 2006IAT 800 Lecture 6 Methods and Classes

Sep 26, Fall 2006IAT 800 Today  A few good programming practices  Methods  Classes –Rockets, asteroids –Subclasses –Methods that return values –BImage

Sep 26, Fall 2006IAT 800 Good Practices  Comments are your friend! –Put a block of commenting at the top of each program that explains what it does –Comment in code what a section will do –Comment when you appropriate code!!  Auto-format is also your friend!!  Your programs will have at least three sections Variable declaration setup() draw()

Sep 26, Fall 2006IAT 800 Methods  Methods, also known as –Functions (methods which return something) –Procedures (methods which don’t return stuff)  Method declaration  Method call void vendingMachine( int coinCents ){ println("You inserted "+coinCents+" cents."); } int quarter = 25; vendingMachine(quarter);

Sep 26, Fall 2006IAT 800 Methods  Method declaration The method declaration is like a blueprint Doesn't matter if declaration is before or after call! Parameter name (e.g. coinCents) is just the name given to data passed into the method… void vendingMachine( int coinCents ){ println("You inserted "+coinCents+" cents."); } void means doesn't return anything parameter

Sep 26, Fall 2006IAT 800 Methods  Method call vendingMachine(quarter) == vendingMachine(25) Method call must occur in either setup(), draw(), or another method… You can call it as many times as you like! –vendingMachine()s for everyone!! int quarter = 25; vendingMachine(quarter); argument

Sep 26, Fall 2006IAT 800 Classes  Types –Primitives: int, float, char, boolean … –Objects: array, string, class …

Sep 26, Fall 2006IAT 800 Objects  We’ve worked with some objects before, like Arrays.  We can make our own objects, to keep related data together, and methods to control that data.

Sep 26, Fall 2006IAT 800 Classes  Classes are the blueprints for our new objects.  To declare a new Class (a new type of object): class MyToy { // fields (class variables) // methods (class functions) }

Sep 26, Fall 2006IAT 800 Fields and Methods class MySquare { int xPos, yPos; MySquare(x, y) { xPos = x; yPos = y; } void drawMe() { rect(xPos, yPos, 50, 50); } xy drawMe() fields constructor methods (one kind of method)

Sep 26, Fall 2006IAT 800 Fields and Methods class MySquare { int xPos, yPos; MySquare(x, y) { xPos = x; yPos = y; } void drawMe() { rect(xPos, yPos, 50, 50); } xy drawMe() MySquare square1 = new MySquare(10, 10); MySquare square2 = new MySquare(20, 90); 10 drawMe() 2090 drawMe() square1square2

Sep 26, Fall 2006IAT 800 Fields and Methods class MySquare { int xPos, yPos; MySquare(int x, int y) { xPos = x; yPos = y; } void drawMe() { rect(xPos, yPos, 50, 50); } MySquare square1 = new MySquare(10, 10); MySquare square2 = new MySquare(20, 90); xy drawMe() 10 drawMe() 2090 drawMe() square1 square2 square1.drawMe(); square2.drawMe();

Sep 26, Fall 2006IAT 800 Arrays of Objects?  Let’s make a bunch of squares! MySquare[] squares = new MySquare [10] ; // initialize all of our squares. for (int i = 0; i < 10; i ++) { squares[i] = new MySquare(i*10, i*10); } squares[4].drawMe(); // draw the 4 th square.

Sep 26, Fall 2006IAT 800 Asteroids  Let’s adapt this to make an array of Asteroids for our rocket from lecture. class Asteroid { //fields float rotation = 0; float xPos, yPos; float velocityX, velocityY; long lastDrawMillis = 0; … }

Sep 26, Fall 2006IAT 800 Asteroids  When we create an asteroid, let’s have it start in a random position, and move in a random direction. Class Asteroid { … // constructor Asteroid() { xPos = random(0, 400); yPos = random(0, 400); rotation = random(0, TWO_PI); velocityX = sin(rotation)*10; velocityY = -cos(rotation)*10; }

Sep 26, Fall 2006IAT 800 Asteroids Class Asteroid { … // draw method void drawMe() {

Sep 26, Fall 2006IAT 800 Revisit our example  So far we have a rocket that flies around in a field of asteroids  What if we want our rocket to be able to fire –But we don’t want to get rid of our non-firing rocket  Create a subclass!

Sep 26, Fall 2006IAT 800 Inheritance  Subclasses inherit fields and methods from parent Class ArmedRocket extends Rocket { … }

Sep 26, Fall 2006IAT 800 Our subclass needs a constructor  Our empty ArmedRocket example creates an error –Processing doesn’t know how to construct an ArmedRocket  We want the ArmedRocket constructor to do the same work as the Rocket constructor ArmedRocket(int initialX, int initialY, float initialRot) { super(initialX, initialY, initialRot); } The keyword super means to call the method in the parent with the same name

Sep 26, Fall 2006IAT 800 Now we have ArmedRocket  We can use an ArmedRocket now in our example  But, it’s basically just a copy of Rocket  The only reason to define an ArmedRocket is to add new capabilities or to override old ones

Sep 26, Fall 2006IAT 800 Add a fire() method  We want our fire method to draw a missile that shoots out of the rocket  We could have the fire method draw the missile… –Is there a problem with this?

Sep 26, Fall 2006IAT 800 Missiles should also be objects  The object oriented solution is to make the missile an object as well –All the different types of “things” in our domain should have a corresponding class  Like asteroids and rockets, the missile class should know how to draw itself –A Missile is similar to a rocket (position, rotation, draw method, etc.)  Now our ArmedRocket.fire() method can just create and return a missile

Sep 26, Fall 2006IAT 800 The fire() method Missile fire() { Missile m = new Missile(xPos, yPos, rotation); return m; }  Now add code in loop to draw missiles

Sep 26, Fall 2006IAT 800 Using the keyPressed() method  keyPressed() is a built in Processing method that is called when a key is pressed  Useful because you can tie events to keystrokes instead of to loop() –If we fire missiles in loop(), notice that we fire many times even if we push the key quickly –This is because loop() is called many times a second