Lecture 6 Methods, Classes, Inheritance IAT 265 Lecture 6 Methods, Classes, Inheritance May 17, 2016 IAT 265

This Lecture Subclasses A few good programming practices Methods Rockets, asteroids Methods that return values Subclasses May 17, 2016 IAT 265

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() May 17, 2016 IAT 265

Methods Methods, also known as Method declaration Method call 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); May 17, 2016 IAT 265

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… parameter void vendingMachine( int coinCents ){ println("You inserted "+coinCents+" cents."); } void means doesn't return anything May 17, 2016 IAT 265

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!! argument int quarter = 25; vendingMachine(quarter); May 17, 2016 IAT 265

Classes Types Primitives: int, float, char, boolean … Objects: array, string, class … May 17, 2016 IAT 265

Objects We’ve worked with some objects before, like Arrays. We can make our own objects, to keep related data together, with methods to control that data. May 17, 2016 IAT 265

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) } May 17, 2016 IAT 265

Fields and Methods class MySquare { int xPos, yPos; MySquare(x, y) { xPos = x; yPos = y; } void drawMe() { rect(xPos, yPos, 50, 50); fields x y constructor drawMe() (one kind of method) methods May 17, 2016 IAT 265

Fields and Methods x y drawMe() 10 10 20 90 drawMe() drawMe() square1 class MySquare { int xPos, yPos; MySquare(x, y) { xPos = x; yPos = y; } void drawMe() { rect(xPos, yPos, 50, 50); 10 10 20 90 drawMe() drawMe() square1 square2 MySquare square1 = new MySquare(10, 10); MySquare square2 = new MySquare(20, 90); May 17, 2016 IAT 265

Fields and Methods square1.drawMe(); square2.drawMe(); x y drawMe() 10 20 90 square1 square2 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); square1.drawMe(); square2.drawMe(); May 17, 2016 IAT 265

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 4th square. May 17, 2016 IAT 265

Asteroids Let’s adapt this to make an array of Asteroids for our rocket from lecture 4 class Asteroid { //fields float rotation = 0; float xPos, yPos; float velocityX, velocityY; long lastDrawMillis = 0; … } May 17, 2016 IAT 265

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; } May 17, 2016 IAT 265

Asteroids class Asteroid { … // draw method void drawMe() { May 17, 2016 IAT 265

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! May 17, 2016 IAT 265

Inheritance Subclasses inherit fields and methods from parent class ArmedRocket extends Rocket { … } May 17, 2016 IAT 265

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 refer to the parent class. In this case, to call the Parent Class Constructor May 17, 2016 IAT 265

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 May 17, 2016 IAT 265

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? May 17, 2016 IAT 265

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 May 17, 2016 IAT 265

The fire() method Now add code in loop to draw missiles Missile fire() { Missile m = new Missile(xPos, yPos, rotation); return m; } Now add code in loop to draw missiles May 17, 2016 IAT 265

Using the keyPressed() method keyPressed() is a built in Processing method that is called when a key is pressed May 17, 2016 IAT 265