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class3.html
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<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>GDI Introduction to Java and OOP Concepts</title>
<meta name="description" content="Intro to Object Oriented Programming with Java curriculum was developed by Ashley Price for Girl Develop It. 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="Girl Develop It">
<meta name="apple-mobile-web-app-capable" content="yes" />
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<link rel="icon" href="images/favicon.ico">
<link rel="stylesheet" href="reveal/css/reveal.css">
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<link rel="stylesheet" href="css/gdi.css">
<!-- For syntax highlighting -->
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<!-- For the slides -->
<link rel="stylesheet" href="css/slides.css">
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<script src="lib/js/html5shiv.js"></script>
<![endif]-->
</head>
<body>
<div class="reveal">
<!-- Any section element inside of this container is displayed as a slide -->
<div class="slides">
<!-- Opening slide -->
<section>
<img src="images/gdi_logo_badge.png" alt="" />
<h3>Intro to Java and OOP Concepts</h3>
<h4>Class 2</h4>
<h5 class='title-page'>Developed for GDI by Ashley Price</h5>
</section>
<!-- Welcome-->
<section>
<h3>Welcome!</h3>
</section>
<section>
<section>
<h3>Review - Variables</h3>
<ul>
<li>Strongly typed</li>
<li>Primatives</li>
<li>Objects</li>
</ul>
</section>
<section>
<h3>Review - Flow Control</h3>
<ul>
<li>Choices</li>
<ul>
<li>If/Else</li>
<li>Switch</li>
</ul>
<li>Loops</li>
<ul>
<li>For Loops</li>
<li>While Loops</li>
</ul>
</ul>
</section>
<section>
<h3>Review - Objects</h3>
<ul>
<li>States - Also called properties and data members.</li>
<li>Behaviors - Actions the object can take. Known as methods.</li>
</ul>
</section>
</section>
<section>
<h3>Agenda</h3>
<ul>
<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>
<h3>Featured Object</h3>
<p>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 of<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>
<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>A Class is a blueprint of an Object.</p>
<p>It tells us how to build an instance of an Object.</p>
<p>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>
<li>File > New > Project</li>
<li>Project name: com.gdi.vehicles</li>
</ol>
</section>
<section>
<h3>Create a new class with a main method</h3>
<ol>
<li>File > New > Class</li>
<li>Class Name: tester</li>
<li>Under <em>which methods would you like to create?</em>, check "public static void main(String[] args)".</li>
</section>
<section>
<h3>Create a new class</h3>
<ol>
<li>File > New > Class</li>
<li>Class Name: MotorVehicle</li>
</ol>
</section>
</section>
<section>
<h3>The Code</h3>
<pre><code class='java'>
public class MotorVehicle {
}
</code></pre>
</section>
</section>
<section>
<section>
<aside class='notes'>
Flip back to our notes and list the data members
</aside>
<h3>Data Members</h3>
<p>An Object has one or more data members that describe its state.</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'>
boolean engineOn;
int currentSpeed;
</code></pre>
</section>
</section>
<section>
<section>
<h3>Defining a Constructor</h3>
<p>When you create an Object, you should include at least one constructor. If you do not, the compiler automatically provides a default one.</p>
<p>A constructor is a special method that is invoked when you create a new instance of your object.</p>
<p>It is common to set default values for your data members in the constructor.</p>
</section>
<section>
<h3>Code It!</h3>
<pre><code class='java'>
public MotorVehicle() {
currentSpeed = 0;
engineOn = false;
}
</code></pre>
</section>
</section>
<section>
<section>
<h3>Defining Methods</h3>
<p>Method represent the behavior of the Objects.</p>
<p>A method signature includes the method's name plus the number and type of paramters.</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>Let's add an accelerated 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>Add a decelerate method that slows the motor vehicle down in decrements of 5</p>
<p>Add a method that will swtich the engine's state</p>
<p><em>If</em> the engine is on turn the engine off</p>
<p><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>
<section>
<section>
<p>You build an Object from a class.</p>
<p>Objects are instances of your classes.</p>
</section>
<section>
<h3>Objects - Creating </h3>
<p>To create an object:</p>
<pre><code class='java'>
ObjectType nameOfInstance = new ObjectType();
</code></pre>
<p>Where ObjectType() is the Object's constructor. If the constructor expects parameters you would include them in this statement: </p>
<pre><code class='java'>
nameOfInstance = new ObjectType(String ex);
</code></pre>
</section>
<section>
<h3>Code It!</h3>
<p>Create a MotorVehicle Object</p>
<p>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>
<section>
<section>
<h3>Using Objects</h3>
<p>Once you have created your object, you can call its different methods with the following format: </p>
<pre><code class='java'>
nameOfInstance.methodName();
</code></pre>
<p>Similarly, you can access data members in this format: </p>
<pre><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>Now use a method of your motor vehicle class: </p>
<ol>
<li>Call switchEngineState to turn on the car.</li>
<li>Print engineOn and confirm it's true.</li>
<li>Print the currentSpeed.</li>
<li>Accelerate the vehicle.</li>
<li>Print the new currentSpeed.</li>
<li>Decelerate the vehicle.</li>
<li>Print the new currentSpeed.</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>Create a method called printDescription that will 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>Test it by calling myVehicle.printDescription();</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>
<section>
<h3>Checkpoint</h3>
<p>Building basic Objects</p>
<ul>
<li>Methods</li>
<li>Data Members</li>
<li>Instances</li>
</ul>
</section>
<section>
<section>
<aside class='notes'>
We've already seen this with the public modifiers on our class declaration and method declaration
</aside>
<h3>Data Members - Access Modifiers</h3>
<p>We can make these data members public or private,</p>
<p>Public members can be accessed by all other classes.</p>
<p>Private memembers can only be accessed within its own class.</p>
</section>
<section>
<h3>Code It!</h3>
<p>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>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>
<h3>What difference does it really make?</h3>
<p>Try running your code again and see.</p>
</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>What is the error we received?</p>
<p>Why did we receive it?</p>
<p>Why is myVehicle.engineOn not throwing the same error?</p>
</section>
</section>
<section>
<section>
<h3>Data Encapsulation</h3>
<p>With OOP, we have the concept of data encapsulation which discourages the direct, public access to a class's data members.</p>
</section>
<section>
<h3>Data Encapsulation</h3>
<p>Data Encapsulation is to hide or restrict direct access to an object's members.</p>
<p>Instead of direct access a set of accessor and modifier methods are used to interact with the data.</p>
</section>
<section>
<h3>Benefits</h3>
<ol>
<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>Let's make all our data members private.</p>
<p>Now we'll need to add accessor methods 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>Add an accessor method to get the current speed: </p>
<pre><code class='java'>
public int getCurrentSpeed() {
return currentSpeed;
}
</code></pre>
<p><span class='individually'>On your own,</span> add an accessor method for the boolean engineOn.</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>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>
<section>
<section>
<h3>Static vs Instance</h3>
<p>When a method is declared static, it is <strong>shared</strong> by all instances of the class.</p>
<p>In contrast, the type of methods we've been using have been <strong>unique</strong> to each instance.</p>
</section>
</section>
<section>
<section>
<aside class='notes'>
The constructor
</aside>
<h3>Static: An Example</h3>
<p>How many cars on the road?</p>
<p>Create a static data member to keep count of the MotorVehicles we've created: </p>
<pre><code class='java'>
private static int countCreated = 0;
</code></pre>
<p>Each time a MotorVehicle is created we want to increment the count.</p>
<p>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>We can create a regular accessor method to return the countCreated.</p>
<pre><code class='java'>
public int getCountCreated() {
return countCreated;
}
</code></pre>
<p><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: " +
myVehicle.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>
<li>Print the result of myVehicle.getCountCreated()</li>
<li>Create a second MotorVehicle myVehicle2</li>
<li>Print the result of myVehicle.getCountCreated()</li>
</ol>
</section>
</section>
<section>
<section>
<h3>Static Method</h3>
<p>Since the <em>countCreated</em> is not specific to the instance, we might want to make a method that is not specific to the instance when accessing the data.</p>
<p>We can create static methods that (like a static data member) is shared by all instance.</p>
</section>
<section>
<h3>Code It</h3>
<p>Add the static keyword to your method declaration: </p>
<pre><code class='java'>
public static int getCountCreated() {
return countCreated;
}
</code></pre>
</section>
<section>
<aside class='notes'>
System.out.println("Number of Vehicles: "+MotorVehicle.getCountCreated());<br>
MotorVehicle myVehicle2 = new MotorVehicle();<br>
System.out.println("Number of Vehicles: "+MotorVehicle.getCountCreated());
</aside>
<h3>Accessing the static method</h3>
<p>You can access a static method the same way you access an instance method, but it is discouraged since it doesn't clearly indicate you accessing a class method.</p>
<p>Instead, we will update our code to use this format: </p>
<pre><code class='java'>
ClassName.staticMethodName();
</code></pre>
</section>
<section>
<h3>The Code</h3>
<pre><code class='java'>
System.out.println("Number of Vehicles: " +
MotorVehicle.getCountCreated());
MotorVehicle myVehicle2 = new MotorVehicle();
System.out.println("Number of Vehicles: " +
MotorVehicle.getCountCreated());
</code></pre>
</section>
</section>
<section>
<h3>Checkpoint</h3>
<ul>
<li>Data Encapsulation</li>
<li>Static vs Instance</li>
</ul>
</section>
<section>
<section>
<h3>Inheritance and Subclasses</h3>
<p>A class can be derived from another class.</p>
<p>A class that is derived from another class is called a <em>subclass</em>.</p>
<p>Subclasses inherit fields and methods from their parent class.</p>
</section>
<section>
<h3>Why would you want it? Inheritance</h3>
<p>New class is created from an existing class.</p>
<p>Reuse code that's already been written.</p>
<p>Can be used to create a hierarchical class structure.</p>
</section>
<section>
<h3>MotorVehicle -> Car</h3>
<p>Let's create a car</p>
<p>File > New > Class</p>
<p>Name: Car</p>
<p>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>
<h3>What you can do with a Subclass</h3>
<p>You can write a subclass constructor that invokes constructor of the superclass.</p>
<p>You can declare new fields in subclass that aren't in the parent class.</p>
<p>Inherited fields can be used directly.</p>
<p>A subclass can't inherit private members.</p>
</section>
</section>
<section>
<section>
<h3>Super</h3>
<p>The Super keyword can be used in a child to call a method or member of the parent class.</p>
<p>The syntax is super.methodName() or super.memberName;</p>
<p>If you want to call the constructor of the super class 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>Create a car constructor that calls super()</p>
</section>
<section>
<h3>The Code</h3>
<pre><code class='java'>
public class Car extends MotorVehicle {
public Car() {
super();
}
}
</code></pre>
</section>
</section>
<section>
<section>
<aside class='notes'>
For instance, while a motor boat doesn't necessarily have a door or a trunk all cars do
</aside>
<h3>What else can you do with a subclass?</h3>
<p>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>
<li>Add a boolean called trunkOpen.</li>
<li>Add an int called numDoors.</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>Our constructor should also be initialize the subclass-only data members.</p>
<p>Initialize trunkOpen to false and numDoors 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>In your tester class:</p>
<ol>
<li>Create a car "myCar".</li>
<li>Turn the engineOn.</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 printDescription.</li>
<li>Print the count of MotorVehicles 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>Add accessor methods for:</p>
<ol>
<li>trunkOpen</li>
<li>numDoors</li>
</ol>
<p>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>
<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>Instance Methods:</p>
<p>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>
<li>In the tester, call the printDescription() method for your car.</li>
<li>Run it.</li>
<li>Create a printDescription() method for your car class that says:<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>The output of myCar.printDescription() now says: </p>
<pre><code class='no-highlight'>
I'm a car! I have 4 doors!
</code></pre>
</section>
</section>
<section>
<section>
<h3>Final Methods</h3>
<p>A Final method cannot be overridden in a subclass.</p>
</section>
<section>
<h3>Test it</h3>
<p>Add the <em>final</em> keyword to the printDescription() method inside of the MotorVehicle class.</p>
<pre><code class='java'>
public final void printDescription() {...}
</code></pre>
<p>The implication is that the subclass, Car, cannot override the printDescription()</p>
<p>Observe the compiler error.</p>
</section>
</section>
<section>
<section>
<h3>A moment to ponder</h3>
<p>Right now we can accelerate and decelrate our car by the default value of "5".</p>
<p>What if we wanted to really slam on the pedal and take a 10 mph jump? Or 20??</p>
<p>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>Doing so is called <em>Method Overloading</em>.</p>
<pre><code class='java'>
public void accelerate(int amount) {
currentSpeed = currentSpeed + amount;
}
</code></pre>
<p>Overloading is summed up by: Same name and different parameter list.</p>
</section>
<section>
<h3>An Error?</h3>
<p><em>The field MotorVehicle.currentSpeed is not visible.</em></p>
<p>We've seen something like this before...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>Inherited Fields.</p>
<p>A subclass can't access a parent's private members.</p>
<p>There is a third access modifier called Protected.</p>
<p>Protected fields can be accessed by subclasses.</p>
</section>
<section>
<h3>Quick Detour</h3>
<p>Hop back to the MotorVehicle class and update your private member "currentSpeed" to protected.</p>
<p>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>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>Assuming a subclass has overloaded a method in the parent class:</p>
<p><em>"When an application needs the function, the particular version is dynamically determined at runtime"</em> - William Ford, William Topp Data Structures with C++ using STL</p>
</section>
<section>
<section>
<h3>Abstraction</h3>
<p>Using the <em>abstract</em> keyword when developing a class indicates that the class will never be instantiated.</p>
<p>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>Abstract classes can contain partial implementations.</p>
<p>Will you ever have just a <em>MotorVehicle</em> on the road?</p>
</section>
<section>
<h3>Code It!</h3>
<p>Convert our MotorVehicle class to an Abstract Class.</p>
<p>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>Now that MotorVehicle is an abstract class, we can't create an instance of it</p>
<p>We have two choices:</p>
<ol>
<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>Since car extends MotorVehicle we can:</p>
<pre><code class='java'>
MotorVehicle myVehicle = new Car();
MotorVehicle myVehicle2 = new Car();
</code></pre>
<p>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>
<h3>Code It!</h3>
<p><span class='individually'>On your own,</span> create a Bus that extends MotorVehicle</p>
<p>Additional Bus specific Methods to include: </p>
<ol>
<li>pickUpPassengers(int numer)</li>