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181 lines
5.6 KiB
HTML
181 lines
5.6 KiB
HTML
<!DOCTYPE html>
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<meta name="author" content="Brandon Rozek">
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<main class="main-content">
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<article class="article">
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<h1>Lecture for March 27</h1>
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<h2>In the Real World...</h2>
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<p>Objects are known for having characteristics. A car has on average 4 wheels, 2-4 doors, a steering wheel.</p>
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<p>Objects can perform actions. A car can drive, hold cargo, and honk.</p>
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<h2>In the Programming World...</h2>
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<p>Object-Oriented Programming</p>
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<ul>
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<li>Focuses on objects</li>
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<li>Are not linear</li>
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<li>Adds organization to a program</li>
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<li>Fits with human cognition (making abstractions)</li>
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</ul>
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<h2>Class Structure</h2>
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<pre><code class="language-java">public class Classname {
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// Fields
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// Constructors
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// Methods
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}</code></pre>
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<h2>Fields</h2>
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<p>Fields are instance variables, they store values, help define state, and exist in memory for the lifetime of the object.</p>
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<pre><code class="language-java">public class Car {
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private double price;
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private double gas;
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}</code></pre>
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<h2>Constructor</h2>
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<p>We can build an object through a constructor. It is a special kind of method, this method requires that you not have a return type and that you name it the same as the class itself.</p>
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<p>Constructors help set default field values for the different properties of our class.</p>
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<pre><code class="language-java">public class Car {
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// Begin Constructor
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public Car(double cost) {
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this.price = cost;
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this.gas = 0;
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}
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// End Constructor
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private double price;
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private double gas;
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}</code></pre>
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<p><strong>Note:</strong> The <code>this</code> keyword refers to the object's fields. This helps keep it separate from other variables you can create in the method and the input parameters you receive.</p>
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<h2>Accessor Method - "Getter"</h2>
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<p>We like to classify methods into two types, accessors and mutators.</p>
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<p>Getter methods return a copy of an instance field. It does not change the state of the object.</p>
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<pre><code class="language-java">public double getPrice() {
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return this.price;
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}</code></pre>
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<h2>Mutator Method - "Setter"</h2>
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<p>This type of method modifies an instance field. It does not return anything and changes the state of the object.</p>
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<pre><code class="language-java">public void setPrice(double cost) {
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this.price = cost;
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}</code></pre>
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<h2>Example of Car Class In All Its Glory</h2>
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<pre><code class="language-java">public class Car {
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// Instance Variables
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private int mpg;
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private double price;
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// Constructors
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public Car() {
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this.price = 0;
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this.mpg = 0;
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}
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public Car(double cost, int mpg) {
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this.price = cost;
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this.mpg = mpg;
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}
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// Accessors
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public double getPrice() {
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return this.price''
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}
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public int getMpg() {
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return this.mpg;
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}
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// Mutators
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public void setPrice(double cost) {
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this.price = cost;
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}
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public void setMpg(int mpg) {
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this.mpg = mpg;
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}
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}</code></pre>
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<h2>Using Classes</h2>
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<p>Just like how we used the <code>Scanner</code> class, we can also use our new <code>Car</code> class.</p>
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<pre><code class="language-java">public class TestCar {
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public static void main(String[] args) {
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// Declare an object reference
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Car c;
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// Initialize the object
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c = new Car();
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// Update the fields of the object
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c.setPrice(3000);
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c.setMpg(22);
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// Print object information
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System.out.println("Price is " + c.getPrice() )
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}
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}</code></pre>
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</article>
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