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2022-02-15 01:14:58 -05:00
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2020-01-15 23:07:02 -05:00
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<h1>Lecture for March 27</h1>
<h2>In the Real World...</h2>
<p>Objects are known for having characteristics. A car has on average 4 wheels, 2-4 doors, a steering wheel.</p>
<p>Objects can perform actions. A car can drive, hold cargo, and honk.</p>
<h2>In the Programming World...</h2>
<p>Object-Oriented Programming</p>
<ul>
<li>Focuses on objects</li>
<li>Are not linear</li>
<li>Adds organization to a program</li>
<li>Fits with human cognition (making abstractions)</li>
</ul>
<h2>Class Structure</h2>
<pre><code class="language-java">public class Classname {
// Fields
// Constructors
// Methods
}</code></pre>
<h2>Fields</h2>
<p>Fields are instance variables, they store values, help define state, and exist in memory for the lifetime of the object.</p>
<pre><code class="language-java">public class Car {
private double price;
private double gas;
}</code></pre>
<h2>Constructor</h2>
<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>
<p>Constructors help set default field values for the different properties of our class.</p>
<pre><code class="language-java">public class Car {
// Begin Constructor
public Car(double cost) {
this.price = cost;
this.gas = 0;
}
// End Constructor
private double price;
private double gas;
}</code></pre>
<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>
<h2>Accessor Method - &quot;Getter&quot;</h2>
<p>We like to classify methods into two types, accessors and mutators.</p>
<p>Getter methods return a copy of an instance field. It does not change the state of the object.</p>
<pre><code class="language-java">public double getPrice() {
return this.price;
}</code></pre>
<h2>Mutator Method - &quot;Setter&quot;</h2>
<p>This type of method modifies an instance field. It does not return anything and changes the state of the object.</p>
<pre><code class="language-java">public void setPrice(double cost) {
this.price = cost;
}</code></pre>
<h2>Example of Car Class In All Its Glory</h2>
<pre><code class="language-java">public class Car {
// Instance Variables
private int mpg;
private double price;
// Constructors
public Car() {
this.price = 0;
this.mpg = 0;
}
public Car(double cost, int mpg) {
this.price = cost;
this.mpg = mpg;
}
// Accessors
public double getPrice() {
return this.price''
}
public int getMpg() {
return this.mpg;
}
// Mutators
public void setPrice(double cost) {
this.price = cost;
}
public void setMpg(int mpg) {
this.mpg = mpg;
}
}</code></pre>
<h2>Using Classes</h2>
<p>Just like how we used the <code>Scanner</code> class, we can also use our new <code>Car</code> class.</p>
<pre><code class="language-java">public class TestCar {
public static void main(String[] args) {
// Declare an object reference
Car c;
// Initialize the object
c = new Car();
// Update the fields of the object
c.setPrice(3000);
c.setMpg(22);
// Print object information
System.out.println("Price is " + c.getPrice() )
}
}</code></pre>
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