Lecture%206%20Methods%20and%20Classes

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IAT 800

• Lecture 6 Methods and Classes

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Today

• A few good programming practices
• Methods
• Classes
• Rockets, asteroids
• Subclasses
• Methods that return values
• BImage

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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()

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Methods

• Methods, also known as
• Functions (methods which return something)
• Procedures (methods which dont return stuff)
• Method declaration
• Method call

void vendingMachine( int coinCents )
println("You inserted "coinCents" cents.")
int quarter 25vendingMachine(quarter)
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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.")
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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 25vendingMachine(quarter)
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Classes

• Types
• Primitives int, float, char, boolean
• Objects array, string, class

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Objects

• Weve worked with some objects before, like
  Arrays.
• We can make our own objects, to keep related data
  together, with methods to control that data.

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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)
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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
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Fields and Methods
class MySquare int xPos, yPos
MySquare(x, y) xPos x yPos y
void drawMe() rect(xPos, yPos, 50, 50)
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10
20
90
drawMe()
drawMe()
square1
square2
MySquare square1 new MySquare(10, 10) MySquare
square2 new MySquare(20, 90)
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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)
square1.drawMe() square2.drawMe()
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Arrays of Objects?

• Lets make a bunch of squares!

MySquare squares new MySquare 10 //
initialize all of our squares. for (int i 0 i
lt 10 i ) squaresi new MySquare(i10,
i10) squares4.drawMe() // draw the 4th
square.
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Asteroids

• Lets 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
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Asteroids

• When we create an asteroid, lets 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
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Asteroids
class Asteroid // draw method void
drawMe()
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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 dont want to get rid of our non-firing
  rocket
• Create a subclass!

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Inheritance

• Subclasses inherit fields and methods from parent
• class ArmedRocket extends Rocket

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Our subclass needs a constructor

• Our empty ArmedRocket example creates an error
• Processing doesnt 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

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Now we have ArmedRocket

• We can use an ArmedRocket now in our example
• But, its basically just a copy of Rocket
• The only reason to define an ArmedRocket is to
  add new capabilities or to override old ones

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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?

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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

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The fire() method

• Missile fire()
• Missile m new Missile(xPos, yPos,
  rotation)
• return m
• Now add code in loop to draw missiles

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Using the keyPressed() method

• keyPressed() is a built in Processing method that
  is called when a key is pressed