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Object-oriented programming is perhaps the dominant development paradigm for leading languages including Java, C#, and Python. The rich class and inheritance framework wasn’t fully implemented in modern PHP until 2015, and best practices for object-oriented programming are still emerging.

This course is an introduction to object-oriented programming in PHP. You’ll start with the basics of the OOP paradigm and get familiar with classes, objects, methods, and properties. You’ll then chain methods and properties using the this keyword before working with access modifiers and magic methods. With these basics down, you’ll take a deep dive into object-oriented programming in PHP, including inheritance, abstraction, polymorphism, and namespaces. After exploring exception handling, you’ll use these object-oriented techniques to build, manage, and edit a PHP database.

By the end of this course, you’ll be prepared to build dynamic server-side applications using object-oriented programming in PHP.

Object-Oriented Programming in PHP

In which  class do we use the `extends` keyword to declare that one class inherits from another class?

In which class do we use the <code>extends</code> keyword to declare that one class inherits from another class?

Which keyword do we use to declare that a method or property can only be used within the parent class and its child classes?

Which keyword do we use to declare that a method or property can only be used within the parent class and its child classes?

Parent class, child class, and global scope


**(Fill in the blank)** The protected access modifier can be accessed in the ________.

(Fill in the blank) The protected access modifier can be accessed in the ________.

**(Fill in the blank)** The private access modifier can be accessed in the ________.

(Fill in the blank) The private access modifier can be accessed in the ________.

What is the output of the following program?
```
<?php 
class Shape {
 private $area = 100;
 protected $type;

 public function display(){
 echo "This is a shape";
 }

 public function getArea(){
 return $this -> $area;
 }
}

class Circle extends Shape {
 public function display() {
 echo "This is a circle and its area is ". $this -> getArea();
 } 
}

class Rectangle extends Shape {

}

$var = new Circle();
$var = new Rectangle();
$var -> display();

?>
```

What is the output of the following program?
<pre><code>&lt;?php 
class Shape {
 private $area = 100;
 protected $type;

 public function display(){
 echo &quot;This is a shape&quot;;
 }

 public function getArea(){
 return $this -&gt; $area;
 }
}

class Circle extends Shape {
 public function display() {
 echo &quot;This is a circle and its area is &quot;. $this -&gt; getArea();
 } 
}

class Rectangle extends Shape {

}

$var = new Circle();
$var = new Rectangle();
$var -&gt; display();

?&gt;
</code></pre>

```
<?php
class A
{
 public $i = 1;
 public $j = 4;

 public function __construct($val) {
 $this -> i += $val;
 }
}
class B extends A
{
 public function __construct($val) {
 $this -> i += $val;
 $this -> i += $this -> j - 2;
 }
}

$a = new A(4);
$a = new B(1);
$a = new B(4);
echo $a -> j;
?>
```
What is the output of the code above?

<pre><code>&lt;?php
class A
{
 public $i = 1;
 public $j = 4;

 public function __construct($val) {
 $this -&gt; i += $val;
 }
}
class B extends A
{
 public function __construct($val) {
 $this -&gt; i += $val;
 $this -&gt; i += $this -&gt; j - 2;
 }
}

$a = new A(4);
$a = new B(1);
$a = new B(4);
echo $a -&gt; j;
?&gt;
</code></pre>
What is the output of the code above?

Let’s practice what we have just learned.

Let’s practice what we have just learned.

Test your understanding of inheritance in PHP.

Introduction

Classes and Objects

Using the $this Keyword for Chaining Methods and Properties

Access Modifiers

Magic Methods and Constants Unveiled

Inheritance in Object-oriented Programming

Abstract Classes and Interfaces

Polymorphism and Type Hinting

Static Methods & Properties and Traits

Namespaces & Dependency Injection

Exception Handling

PHP Database

Model-view-controller (MVC)

Conclusion

Appendix

Quiz: Inheritance