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<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>Introduction to Java and OOP Concepts | Girl Develop It Ann Arbor</title>
<meta name="description" content="Intro to Object Oriented Programming with Java curriculum was developed by Ashley Price for Girl Develop It, and modified by Julie Cameron and Steve Coffey. The course is meant to be taught in 2 4-hour sections. The slides are customizable according to the needs of a given class or audience.">
<meta name="author" content="Ashley Price">
<meta name="apple-mobile-web-app-capable" content="yes" />
<meta name="apple-mobile-web-app-status-bar-style" content="black-translucent" />
<link rel="shortcut icon" href="favicon.ico">
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<link rel="stylesheet" href="lib/css/rainbow.css">
<link rel="stylesheet" href="css/print/pdf.css" media="print">
<script src="lib/js/head.min.js"></script>
<!--[if lt IE 9]>
<script src="lib/js/html5shiv.js"></script>
<![endif]-->
</head>
<body>
<div class="reveal">
<div class="slides">
<!-- EVENT INTRO -->
<section>
<section>
<img src="images/gdi_logo_badge.png" class="img--bare" height="450px" />
<div class="box--small">
<h3 class="event__title"><span class="green">Intro to Java</span><br /><small><span class="blue">& Object Oriented Programming</span></small></h3>
<p><small>@gdiannarbor | #GDIA2 | #IntroToJava</small></p>
<aside class="notes">
</aside>
</div>
</section>
<section>
<h3>Review: <span class="blue">Variables</span></h3>
<ul class="list--tall copy--small box--small">
<li>Statically typed</li>
<li>Strongly typed</li>
<li>Primitives</li>
<li>Objects</li>
</ul>
</section>
<section>
<h3>Review: <span class="blue">Flow Control</span></h3>
<ul class="list--tall copy--small box--small">
<li>Choices
<ul class="copy--small">
<li>If/Else</li>
<li>Switch</li>
</ul>
</li>
<li>Loops
<ul class="copy--small">
<li>For Loops</li>
<li>While Loops</li>
</ul>
</li>
</ul>
</section>
<section>
<h3>Review: <span class="blue">Objects</span></h3>
<ul class="list--tall box--small copy--small">
<li><strong>States</strong> - Also called properties and data members</li>
<li><strong>Behaviors</strong> - actions the object can take. Known as methods</li>
</ul>
</section>
<section>
<h3>Agenda</h3>
<ul class="list--tall box--small copy--small">
<li>Objects and Classes</li>
<li>Defining Fields and Methods</li>
<li>Data Encapsulation</li>
<li>Subclasses and Inheritance</li>
<li>Polymorphism</li>
<li>Abstraction</li>
<li>Interfaces</li>
</ul>
</section>
</section>
<!-- Featured Object -->
<section>
<section>
<h3>Featured Object</h3>
<p class="copy--small box">MotorVehicles which are types of Vehicles and include cars and buses</p>
</section>
<section>
<aside class='notes'>
Create an "Interface" based on this discussion<br>
Have an engine whose state can be on or off<br>
you can turn an engine on<br>
you can turn an engine off<br>
------<br>
Have a current speed<br>
accelerate<br>
decelerate<br>
check your current speed -- accessor method<br>
------<br>
Potential additional members: <br>
color<br>
maximum number of passengers -- accessor method<br>
current number of passengers -- accessor method<br>
</aside>
<p>Describe a Motor Vehicle's states and behaviors</p>
</section>
</section>
<!-- Classes -->
<section>
<section>
<aside class='notes'>
Think of how with a single recipe you can create cookies MANY times...<br>
Note to self: Bring cookies to class
</aside>
<h3>Classes</h3>
<p class="copy--small box--small">A <span class="blue">Class</span> is a <span class="green">blueprint of an Object</span></p>
<p class="copy--small fragment box--small">It tells us how to build an <em>instance</em> of an Object.</p>
<p class="copy--small fragment box--small">From one blueprint, we can create many instances of a single Object</p>
</section>
<section>
<h3>Class Declarations</h3>
<p>When defining a class you must include: </p>
<pre><code class='java'>
class ClassName {
...
}
</code></pre>
</section>
<section>
<h3>Create a new project</h3>
<ol class="list--tall box">
<li>File > New > Project</li>
<li>Project name: com.gdi.vehicles</li>
</ol>
</section>
<section>
<h4>Create a new class with a main method</h4>
<ol class="list--tall box copy--small">
<li>File > New > Class</li>
<li>Class Name: Tester</li>
<li>Don't forget to add to add our main function:<br/> <code>public static void main(String[] args)</code></li>
</section>
<section>
<h3>Create a new class</h3>
<ol class="list--tall box">
<li>File > New > Class</li>
<li>Class Name: MotorVehicle</li>
</ol>
</section>
<section>
<h3>The Code</h3>
<pre><code class='java'>
public class MotorVehicle {
}
</code></pre>
</section>
</section>
<!-- Data Members -->
<section>
<section>
<aside class='notes'>
Flip back to our notes and list the data members
</aside>
<h3>Data Members</h3>
<p class="box copy--small">An Object has one or more <span class="blue">data members</span> that <span class="green">describe its state</span>.</p>
</section>
<section>
<aside class='notes'>
public class MotorVehicle {<br>
boolean engineOn;<br>
int currentSpeed;<br>
int maxNumberPassengers;<br>
int numCurrentPassengers;<br>
}<br>
</aside>
<h3>Defining Data Members</h3>
<pre><code class='java'>
public class MotorVehicle {
boolean engineOn;
int currentSpeed;
}
</code></pre>
</section>
</section>
<!-- Constructors -->
<section>
<section>
<h3>Defining a Constructor</h3>
<p class="copy--small box fragment">A constructor is a special method that is invoked<br/>when you create a new instance of your object.</p>
<p class="copy--xsmall box fragment">It's common to set default values for your data members in the constructor</p>
<p class="copy--xsmall box fragment">When you create an Object, you should include at least one constructor. <br/>If you do not, the compiler automatically provides a default one.</p>
</section>
<section>
<h3>Code It!</h3>
<pre><code class='java'>
public MotorVehicle() {
currentSpeed = 0;
engineOn = false;
}
</code></pre>
</section>
</section>
<!-- Methods -->
<section>
<section>
<h3>Defining Methods</h3>
<p class="copy--small box"><span class="blue">Methods</span> represent the <span class="green">behavior of the Objects</span>.</p>
<p class="copy--xsmall fragment box">A method signature includes the method's name plus the number and type of parameters</p>
</section>
<section>
<aside class='notes'>
addPassenger?<br>
removePassenger?
</aside>
<h3>MotorVehicle Methods</h3>
<pre><code class='java'>
public void accelerate();
public void decelerate();
</code></pre>
</section>
<section>
<h3>Code It! (Adding Methods)</h3>
<p class="copy--small box--small">Let's add an accelerate method to our MotorVehicle class: </p>
<pre><code class='java'>
public void accelerate() {
currentspeed = currentspeed + 5;
}
</code></pre>
</section>
<section>
<aside class='notes'>
void decelerate(){<br>
currentSpeed = currentSpeed - 5;<br>
}<br>
<br>
switchEngineState() {<br>
if(engineOn == true) {<br>
engineOn = false;
} else { <br>
engineOn = true;
}<br>
<br>
void addPassenger(){<br>
currentNumPassengers++;<br>
}<br>
<br>
void removePassenger{<br>
currentNumPassengers--;<br>
}
</aside>
<h3><span class='individually'>Individually</span></h3>
<p class="copy--small box--small">Add a decelerate method that slows the motor vehicle down in increments of 5.</p>
<p class="copy--small box--small">Add a method that will swtich the engine's state</p>
<p class="copy--small box--small"><em>If</em> the engine is on turn the engine off</p>
<p class="copy--small box--small"><em>else</em> the engine is off so turn the engine on</p>
</section>
<section>
<h3>The Code</h3>
<pre><code class='java'>
public void decelerate() {
currentSpeed = currentSpeed - 5;
}
public void switchEngineState() {
if (engineOn == true) {
engineOn = false;
}
else {
engineOn = true;
}
}
</code></pre>
</section>
</section>
<!-- Objects -->
<section>
<section>
<h3>Objects</h3>
<p class="box">You build an Object from a class</p>
<p class="box">Objects are instances of your classes</p>
</section>
<section>
<h3>Objects - Creating </h3>
<p class="copy--small box--small">To create an object:</p>
<pre style="height: 80px; overflow: hidden"><code class='java'>
MyObject obj = new MyObject();
</code></pre>
<p class="copy--small box--small">where <code>new MotorVehicle()</code> is the constructor we just wrote.
<p class="copy--small box--small">If the constructor expects parameters<br/>you would include them in this statement: </p>
<pre style="height: 120px; overflow: hidden"><code class='java'>
ComplexClass myComplexClass =
new ComplexClass("This constructor takes a string");
</code></pre>
</section>
<section>
<h3>Code It!</h3>
<p class="copy--small box--small">Create a MotorVehicle Object</p>
<p class="copy--small box--small">In the main method of the Tester class, add the following line: </p>
<pre><code class='java'>
MotorVehicle myVehicle = new MotorVehicle();
</code></pre>
</section>
<section>
<h3>Using Objects</h3>
<p class="copy--small box--small">Once you have created your object, you can call its different methods with the following format: </p>
<pre style="height: 80px; overflow: hidden"><code class='java'>
nameOfInstance.methodName();
</code></pre>
<p class="copy--small box--small">Similarly, you can access data members in this format: </p>
<pre style="height: 80px; overflow: hidden"><code class='java'>
nameOfInstance.datamember;
</code></pre>
</section>
<section>
<aside class='notes'>
MotorVehicle myVehicle = new MotorVehicle();<br>
myVehicle.switchEngineState();<br>
System.out.println("Engine is On: "+myVehicle.engineOn);<br>
System.out.println("Current Speed: "+myVehicle.currentSpeed);<br>
myVehicle.accelerate();<br>
System.out.println("Current Speed: "+myVehicle.currentSpeed);<br>
myVehicle.decelerate();<br>
System.out.println("Current Speed: "+myVehicle.currentSpeed);<br>
<br>
<strong>output:</strong><br>
Engine is on: true<br>
Current Speed: 0<br>
Current Speed: 5<br>
Current Speed: 0
</aside>
<h3>Code It!</h3>
<p class="copy--small box--small">Now use a method of your motor vehicle class: </p>
<ol class="list--tall copy--xsmall">
<li>call <code>switchEngineState</code> to turn on the car</li>
<li>Print <code>engineOn</code> and confirm it's true</li>
<li>Print the <code>currentSpeed</code></li>
<li>Accelerate the vehicle</li>
<li>Print the new <code>currentSpeed</code></li>
<li>Decelerate the vehicle</li>
<li>Print the new <code>currentSpeed</code></li>
</ol>
</section>
<section>
<h3>The Code</h3>
<pre><code class='java'>
MotorVehicle myVehicle = new MotorVehicle();
myVehicle.switchEngineState();
System.out.println("Engine is on: " + myVehcile.EngineOn);
System.out.println("Current Speed: " + myVehicle.currentSpeed);
myVehicle.accelerate();
System.out.println("Current Speed: " + myVehicle.currentSpeed);
myVehicle.decelerate();
System.out.println("Current Speed: " + myVehicle.currentSpeed);
</code></pre>
<p>Output:</p>
<pre><code class='no-highlight'>
Engine is on: true
Current Speed: 0
Current Speed: 5
Current Speed: 0
</code></pre>
</section>
<section>
<aside class='notes'>
public void printDescription(){<br>
System.out.println("I'm a Motor Vehicle and my Engine is on "+engineOn+" and i'm going "+currentSpeed+"mph");<br>
}<br>
</aside>
<h3><span class='individually'>Individually</span></h3>
<p class="copy--small box--small">Create a method called <code>printDescription</code> that will<br/>print the following statement:</p>
<pre><code class='no-highlight'>
I'm a MotorVehicle and my engine is on (true/false) and
I'm currently going (#)mph.
</code></pre>
<p class="copy--small box--small">Test it by calling <code>myVehicle.printDescription();</code></p>
</section>
<section>
<h3>The Code</h3>
<pre><code class='java'>
public void printDescription () {
System.out.println("I'm a MotorVehicle and my engine is on " +
engineOn + " and I'm currently going " +
currentSpeed + " mph.");
}
</code></pre>
</section>
</section>
<!-- QUESTIONS / Break -->
<section>
<section>
<h3>Questions?</h3>
<p class="box--small">Objects & Classes</p>
<p class="box--small">Methods, Data Members, & Instances</p>
</section>
<section>
<h3>Break Time!</h3>
</section>
<section>
<h3>Review / Questions?</h3>
<p class="box--small">Objects & Classes</p>
<p class="box--small">Methods, Data Members, & Instances</p>
</section>
</section>
<!-- Data Members -->
<section>
<section>
<aside class='notes'>
We've already seen this with the public modifiers on our class declaration and method declaration
</aside>
<h4>Data Members - Access Modifiers</h4>
<p class="box copy--small">We can make these data members public or private</p>
<p class="box copy--small">Public members can be accessed by all other classes</p>
<p class="box copy--small">Private members can only be accessed within its own class</p>
</section>
<section>
<h3>Code It!</h3>
<p class="copy--small box--small">Mark your data members public and private</p>
<pre><code class='java'>
public boolean engineOn;
private int currentSpeed;
</code></pre>
</section>
<section>
<h3>Accessing Data Members</h3>
<p class="copy--small box--small">If your fields are declared with the <em>public</em> access modifier you can access the data members directly with the format mentioned before: </p>
<pre><code class='java'>
instanceOfObject.fieldName
</code></pre>
</section>
<section>
<aside class='notes'>
The field MotorVehicle.currentSpeed is not visible<br>
b/c currentSpeed is now private<br>
b/c it's public
</aside>
<h3>Oops!</h3>
<p class="copy--small box">What is the error we received?</p>
<p class="copy--small box">Why did we receive it?</p>
<p class="copy--small box">Why is <code>myVehicle.engineOn</code> not throwing the same error?</p>
</section>
</section>
<!-- Data Encapsulation -->
<section>
<section>
<h3>Data Encapsulation</h3>
<p class="copy--small box">With OOP, we have the concept of <strong>data encapsulation</strong> which discourages the direct, public access to a class's data members.</p>
</section>
<section>
<h3>Data Encapsulation</h3>
<p class="copy--small box"><strong>Data Encapsulation</strong> is to hide or restrict direct access<br/>to an object's members</p>
<p class="copy--xsmall box">Instead of direct access a set of accessor and modifier methods<br/>are used to interact with the data.</p>
</section>
<section>
<h3>Benefits</h3>
<ol class="list--tall box--small copy--small">
<li>Control to make fields read-only and write-only</li>
<li>Classes can have absolute control over what is stored in the field</li>
<li>Provides a layer of abstraction. Users of the class (other code or objects) do not need to know the details of the data storage</p>
</ol>
</section>
<section>
<aside class='notes'>
Change from public to private:<br>
private boolean engineOn;
</aside>
<h3>Encapsulating our Data</h3>
<p class="copy--small box--small">Let's make all our data members private</p>
<p class="copy--small box--small">Now we'll need to add accessor methods<br/>so we can still access the data</p>
</section>
<section>
<aside class='notes'>
public boolean getEngineOn(){<br>
return engineOn;<br>
}<br>
</aside>
<h3>Code It!</h3>
<p class="copy--small box--small">Add an accessor method to get the current speed: </p>
<pre><code class='java'>
public int getCurrentSpeed() {
return currentSpeed;
}
</code></pre>
<p class="copy--small box--small"><span class='individually'>On your own,</span> add an accessor method for the boolean <code>engineOn</code></p>
</section>
<section>
<pre><code class='java'>
public boolean getEngineOn() {
return engineOn;
}
</code></pre>
</section>
<section>
<aside class='notes'>
System.out.println("Engine is On: "+myVehicle.getEngineOn());<br>
System.out.println("Current Speed: "+myVehicle.getCurrentSpeed());<br>
myVehicle.accelerate();<br>
System.out.println("Current Speed: "+myVehicle.getCurrentSpeed());<br>
myVehicle.decelerate();<br>
System.out.println("Current Speed: "+myVehicle.getCurrentSpeed());<br>
</aside>
<h3>Update our Code</h3>
<p class="copy--small box--small">Now instead of calling on your data members directly, use the accessor methods we just created to get their values.</p>
<pre><code class='java'>
System.out.println("Current Speed: " + myVehicle.getCurrentSpeed());
</code></pre>
</section>
</section>
<!-- Static -->
<section>
<section>
<h3>Static vs Instance</h3>
<p class="copy--small box">When a method is declared static,<br/>it is <strong>shared</strong> by all instances of the class.</p>
<p class="copy--small box">In contrast, the type of methods we've been using<br/>have been <strong>unique</strong> to each instance.</p>
</section>
<section>
<aside class='notes'>
The constructor
</aside>
<h3>Static: An Example</h3>
<p class="copy--small box--small">How many cars on the road?</p>
<p class="copy--small box--small">Create a static data member to keep count of<br/>the MotorVehicles we've created: </p>
<pre style="height: 130px; overflow: hidden;"><code class='java'>
private static int countCreated = 0;
</code></pre>
<p class="copy--small box--small">Each time a MotorVehicle is created we want to increment the count.</p>
<p class="copy--small box--small">Where would we put the code to do so?</p>
</section>
<section>
<h3>Code It</h3>
<pre><code class='java'>
public MotorVehicle() {
currentSpeed = 0;
engineOn = false;
countCreated++;
}
</code></pre>
</section>
<section>
<h3>Add an Accessor</h3>
<p class="copy--small box--small">We can create a <em>static</em> accessor method to return the <code>countCreated</code>.</p>
<p class="copy--small box--small">Since this method belongs to the <em>class</em> and not an instance of the class, we call the method on the MotorVehicle class</p>
<pre><code class='java'>
public static int getCountCreated() {
return countCreated;
}
</code></pre>
<p class="copy--small box--small"><span class='individually'>On your own,</span> print the countCreated</p>
</section>
<section>
<h3>The Code</h3>
<pre><code class='java'>
System.out.println("Number of vehicles on the road: " +
MotorVehicle.getCountCreated());
</code></pre>
</section>
<section>
<aside class='notes'>
Note that they are the same because they are referencing the same data member
</aside>
<h3>Testing our Static Data Member</h3>
<ol class="list--tall copy--small box--small">
<li>Create a second MotorVehicle myVehicle2</li>
<li>Print the result of <code>MotorVehicle.getCountCreated()</code></li>
<li>Print the result of <code>MotorVehicle.getCountCreated()</code></li>
</ol>
</section>
</section>
<!-- QUESTIONS / Break -->
<section>
<section>
<h3>Questions?</h3>
<p class="box--small">Data Encapsulation</p>
<p class="box--small">Static vs Instance</p>
</section>
<section>
<h3>Break Time!</h3>
</section>
<section>
<h3>Review / Questions?</h3>
<p class="box--small">Data Encapsulation</p>
<p class="box--small">Static vs Instance</p>
</section>
</section>
<!-- Subclass -->
<section>
<section>
<h3>Inheritance and Subclasses</h3>
<p class="box copy--small">A class can derive from another class</p>
<p class="box copy--small">A class that is derived from another class is called a <em>subclass</em></p>
<p class="box copy--small">Subclasses inherit fields and methods from their parent class</p>
</section>
<section>
<h4>Why would you want it? Inheritance</h4>
<ul class="copy--small list--tall box--small">
<li>New class is created from an existing class</li>
<li>Reuse code</li>
<li>Can be used to create a hierarchical class structure</li>
</ul>
</section>
<section>
<h3>MotorVehicle -> Car</h3>
<p class="copy--small box--small">Let's create a car</p>
<p class="copy--small box--small">File > New > Class</p>
<p class="copy--small box--small">Name: Car</p>
<p class="copy--small box--small">Add the extends keyword and the name of the parent class (MotorVehicle)</p>
<pre><code class='java'>
public class Car extends MotorVehicle {
...
}
</code></pre>
</section>
<section>
<h4>What can you do with a Subclass?</h4>
<p class="copy--small fragment box--small">You can write a subclass constructor that<br/>invokes the constructor of the superclass</p>
<p class="copy--small fragment box--small">You can declare new fields in the subclass<br/> that aren't in the parent class</p>
<p class="copy--small fragment box--small">Inherited fields can be used directly</p>
<p class="copy--small fragment box--small">A subclass can't inherit private members</p>
</section>
</section>
<!-- Super -->
<section>
<section>
<h3>Super</h3>
<p class="copy--small box--small">The <code>super</code> keyword can be used in a child<br/>to call a method or member of the parent class</p>
<p class="copy--small box--small">The syntax is <code>super.methodName()</code> or <code>super.memberName;</code></p>
<p class="copy--small box--small">If you want to call the constructor of the super class,<br/> you simply use the syntax: </p>
<pre><code class='java'>
super();
</code></pre>
</section>
<section>
<aside class='notes'>
public Car(){<br>
super();<br>
}
</aside>
<h3>Code It!</h3>
<p class="copy--small box">Create a car constructor that calls <code>super()</code></p>
</section>
<section>
<h3>The Code</h3>
<pre><code class='java'>
public class Car extends MotorVehicle {
public Car() {
super();
}
}
</code></pre>
</section>
</section>
<!-- More subclass -->
<section>
<section>
<aside class='notes'>
For instance, while a motor boat doesn't necessarily have a door or a trunk all cars do
</aside>
<h4>What else can you do with a subclass?</h4>
<p class="copy--small box">You can declare new fields in subclass that aren't in the parent class.</p>
</section>
<section>
<aside class='notes'>
public class Car extends MotorVehicle {<br>
<strong>private boolean trunkOpen;<br>
private int numDoors;</strong><br>
public Car() {<br>
super();<br>
}<br>
}
</aside>
<h3>Code It!</h3>
<ol class="list--tall box--small copy--small">
<li>Add a boolean called <code>trunkOpen</code></li>
<li>Add an int called <code>numDoors</code></li>
</ol>
</section>
<section>
<h3>The Code</h3>
<pre><code class='java'>
public class Car extends MotorVehicle {
private boolean trunkOpen;
private int numDoors;
public Car() {
super();
}
}
</code></pre>
</section>
<section>
<aside class='notes'>
public Car() {<br>
super();<br>
<strong>trunkOpen = false;<br>
numDoors = 4;</strong><br>
}
</aside>
<h3>Augment the constructor</h3>
<p class="copy--small box">Our constructor should also initialize the subclass-only data members</p>
<p class="copy--small box">Initialize <code>trunkOpen</code> to false and <code>numDoors</code> to 4</p>
</section>
<section>
<h3>The Code</h3>
<pre><code class='java'>
public class Car extends MotorVehicle {
private boolean trunkOpen;
private int numDoors;
public Car() {
super();
trunkOpen = false;
numDoors = 4;
}
}
</code></pre>
</section>
<section>
<aside class='notes'>
Car myCar = new Car();<br>
myCar.switchEngineState();<br>
System.out.println(myCar.getCurrentSpeed());<br>
myCar.accelerate();<br>
System.out.println(myCar.getCurrentSpeed());<br>
myCar.printDescription();<br>
System.out.println("Number of Vehicles: "+MotorVehicle.getCountCreated());
</aside>
<h3>Test it Out</h3>
<p class="copy--small box--small">In your HelloWorld class:</p>
<ol class="list--tall copy--small box--small">
<li>Create a car "myCar"</li>
<li>Turn the <code>engineOn</code></li>
<li>Print the car's current speed</li>
<li>Accelerate the car</li>
<li>Print the car's new current speed</li>
<li>Call <code>printDescription</code></li>
<li>Print the count of <code>MotorVehicles</code> on the road</li>
</ol>
</section>
<section>
<aside class='notes'>
Highlight that we now have 3 motor vehicles<br>
Trace through calling the parent's constructor and methods<br>
Car must be rolling down the street...someone forgot the emergency break
</aside>
<h3>The Code</h3>
<pre><code class='java'>
Car myCar = new Car();
myCar.switchEngineState();
System.out.println(myCar.getCurrentSpeed());
myCar.accelerate();
System.out.println(myCar.getCurrentSpeed());
myCar.printDescription();
System.out.println("Number of Vehicles on the road: " +
MotorVehicle.getCountCreated());
</code></pre>
<p>Output:</p>
<pre><code class='no-highlight'>
0
5
I'm a Motor Vehicle and my Engine is on true and I'm going 5 mph
Number of Vehicles on the road: 3
</code></pre>
</section>
<section>
<h3><span class='individually'>Individually</span></h3>
<p class="copy--small box--small">Add accessor methods for:</p>
<ol class="list--tall copy--xsmall">
<li><code>trunkOpen</code></li>
<li><code>numDoors</code></li>
</ol>
<p class="copy--small box--small">Call the methods in the Tester</p>
</section>
<section>
<h3>Code</h3>
<pre><code class='java'>
public boolean getTrunkOpen() {
return trunkOpen;
}
public int getNumDoors() {
return numDoors;
}
</code></pre>
<pre><code class='java'>
System.out.println("number doors: " + myCar.getNumDoors());
System.out.println("the trunk is open: " + myCar.getTrunkOpen());
</code></pre>
</section>
</section>
<!-- Overrides -->
<section>
<section>
<aside class='notes'>
Optionally have the @Override notation<br>
Potentially useful since it shows up in all my android projects a # of times..
</aside>
<h3>Overriding Methods</h3>
<p class="copy--small box--small">Instance Methods:</p>
<p class="copy--small box--small">An instance method in a subclass (child class) that has the same signature and return type as an instance method in the superclass <em>overrides</em> the superclass's method.</p>
</section>
<section>
<h3>Code It</h3>
<ol class="list--tall copy--small box--small">
<li>In the Tester, call the <code>printDescription()</code> method for your car</li>
<li>Run it</li>
<li>Create a <code>printDescription()</code> method for your car class that says:<br/><em>
I'm a car! I have (#) doors!</em></li>
</ol>
</section>
<section>
<aside class='notes'>
If we comment out the printDescription() code in Car, the code calls the printDescription() of the parent class<br>
uncomment and it uses the car<br>
Any questions?
</aside>
<h3>Overriding Methods Cont.</h3>
<p class="copy--small box--small">The output of <code>myCar.printDescription()</code> now says: </p>
<pre><code class='no-highlight'>
I'm a car! I have 4 doors!
</code></pre>
</section>
</section>
<!-- Final methods -->
<section>
<section>
<h3>Final Methods</h3>
<p class="copy--small box">A Final method cannot be overridden in a subclass</p>
</section>
<section>
<h3>Test it</h3>
<p class="copy--small box--small">Add the <em>final</em> keyword to the <code>printDescription()</code> method<br/> inside of the MotorVehicle class</p>
<pre><code class='java'>
public final void printDescription() {...}
</code></pre>
<p class="copy--small box--small">The implication is that the subclass, Car,<br/>cannot override the <code>printDescription()</code></p>
<p class="copy--small box--small">What happens?</p>
</section>
</section>
<!-- Method Overloading -->
<section>
<section>
<h3>A moment to ponder</h3>
<p class="copy--small box">Right now we can accelerate and decelrate<br/>our car by the default value of "5"</p>
<p class="copy--small box">What if we wanted to really slam on the pedal<br/>and take a 10 mph jump? Or 20??</p>
<p class="copy--small box fragment">We can create another accelerate/decelerate method that will take a parameter specifying how much faster or slower we want to go</p>
</section>
<section>
<h3>Method Overloading</h3>
<p class="copy--small box--small">Doing so is called <em>Method Overloading</em></p>
<pre><code class='java'>
public void accelerate(int amount) {
currentSpeed = currentSpeed + amount;
}
</code></pre>
<p class="copy--small box--small">Overloading is summed up by:<br/>Same name and different parameter list</p>
</section>
<section>
<h3>An Error?</h3>
<p class="copy--small box"><em>The field MotorVehicle.currentSpeed is not visible</em></p>
<p class="copy--small box">We've seen something like this before...<br/>it has to do with those access modifiers</p>
</section>
</section>
<section>
<section>
<aside class='notes'>
Protected is also accessed by classes in the same package
</aside>
<h3>Fields</h3>
<p class="copy--small box--small">Inherited Fields</p>
<p class="copy--small fragment box--small">A subclass can't access a parent's private members</p>
<p class="copy--small fragment box--small">There is a third access modifier called Protected</p>
<p class="copy--small fragment box--small">Protected fields can be accessed by subclasses</p>
</section>
<section>
<h3>Quick Detour</h3>
<p class="copy--small box--small">Hop back to the MotorVehicle class and update your private member <code>currentSpeed</code> to protected.</p>
<p class="copy--small box--small">Now that the error has gone, test out your new method: </p>
<pre><code class='java'>
myCar.accelerate(10);
System.out.println(myCar.getCurrentSpeed());
</code></pre>
</section>
<section>
<h3><span class='individually'>Individually</span></h3>
<p class="copy--small box">Overload the decelerate method in the same fashion</p>
</section>
<section>
<h3>The Code</h3>
<pre><code class='java'>
public void decelerate(int amount) {
currentSpeed = currentSpeed - amount;
}
</code></pre>
</section>
</section>
<section>
<aside class='notes'>
Polymorphism can be a bit of an advanced topic since it's really covers a lot of ground with various types<br>
We want to mention it so they can say "ooooh yeah I've heard of that" not much to do with it in java
</aside>
<h3>Polymorphism</h3>
<p class="copy--small box">Assuming a subclass has overloaded a method in the parent class:</p>
<p class="copy--small box--small"><em>"When an application needs the function, the particular<br/>version is dynamically determined at runtime"</em><br/><small>William Ford, William Topp Data Structures with C++ using STL</small></p>
</section>
<section>
<section>
<h3>Abstraction</h3>
<p class="copy--small box--small">Using the <code>abstract</code> keyword when developing a class indicates that the class will never be instantiated directly</p>
<p class="copy--small box--small">However, other classes that extend (inherit) the abstract class (if not abstract themselves) could be instantiated</p>
</section>
<section>
<aside class='notes'>
No<br>
You have cars<br>
Trucks<br>
Buses<br>
But nothing that's just a generic MotorVehicle
</aside>
<h3>Building an Abstract Class</h3>
<p class="copy--small box--small">Abstract classes can contain partial implementations</p>
<p class="copy--small box--small">Will you ever have just a <em>MotorVehicle</em> on the road?</p>
</section>
<section>
<h3>Code It!</h3>
<p class="copy--small box--small">Convert our MotorVehicle class to an Abstract Class</p>
<p class="copy--small box--small">Add the <em>abstract</em> keyword to the class declaration:</p>
<pre><code class='java'>
public abstract class MotorVehicle { ... }
</code></pre>
</section>
<section>
<h3>Updating our Tests</h3>
<p class="copy--small box--small">Now that MotorVehicle is an abstract class,<br/>we can't create an instance of it</p>
<p class="copy--small box--small">We have two choices:</p>
<ol class="list--tall copy--xsmall">
<li>Comment out the code</li>
<li>Update the code to create instances of Cars</li>
</ol>
</section>
<section>
<aside class='notes'>
Flexibility -- MotorVehicle could be used as a parameter in methods and any MotorVehicle (regardless of subtype) could be passed when declared like this<br>
<br>
Polymorphism
</aside>
<h3>Updating Cont.</h3>
<p class="copy--small box--small">Since car extends MotorVehicle we can:</p>
<pre><code class='java'>
MotorVehicle myVehicle = new Car();
MotorVehicle myVehicle2 = new Car();
</code></pre>
<p class="copy--small box--small">Why would you want to do this?</p>
</section>
</section>
<section>
<aside class='notes'>
Hiding really only matters if you used the parent class type when declaring a new instace of a subclass<br>
i.e.<br>
MotorVehicle myOtherCar = new Car();<br>
<br>
If we call myOtherCar.staticMethod() it will look at the declared type "MotorVehicle" and call that static method
</aside>
<!--
<h3>Hiding Methods</h3>
<p>Class Methods:</p>
<p>If a subclass defines a class method with the same signature as a class method in the superclass, the method in the subclass hides the one in the superclass</p>
</section>
<section>
-->
<aside class='notes'>
Give them plenty of time to play around with creating their own subclass<br>
Encourage them to use the concepts discussed
</aside>