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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

Which keyword is used to declare a class or method as abstract?

Which keyword is used to declare a class or method as abstract?

Which keyword is used to declare a child class that inherits from an abstract class?

Which keyword is used to declare a child class that inherits from an abstract class?

To commit the child classes to certain methods.

To make a good impression on your boss and colleagues.

To encapsulate the code of the parent class from any outside code outside.

**(True or False)** We can create objects from abstract classes.

(True or False) We can create objects from abstract classes.

Which keyword should we use to implement an interface?

Which keyword should we use to implement an interface?

Which of the following code types are allowed in an interface?

Which of the following code types are allowed in an interface?

Which access modifier is allowed for abstract methods in interfaces?

Which access modifier is allowed for abstract methods in interfaces?

A class can inherit from an abstract class and two interfaces.

A class can inherit from a parent class and one interface.

A class can inherit from a parent class and more than one interface.

A class can inherit from two abstract classes.

Which option is an example of a valid inheritance?

Which option is an example of a valid inheritance?

What is the output of the following code?
```
<?php 
abstract class Chair {
 protected $weight;

 public function setWeight($chairWeight) {
 $this -> weight = $chairWeight;
 }

 abstract public function calcChairPrice();
 abstract public function displayChair(); 
}

class WoodChair extends Chair {
 public function calcChairPrice() {
 return $this -> weight * 100;; 
 }
}

$chair = new WoodChair();
$chair -> setWeight(20);
echo $chair -> calcChairPrice();
?>
```

What is the output of the following code?
<pre><code>&lt;?php 
abstract class Chair {
 protected $weight;

 public function setWeight($chairWeight) {
 $this -&gt; weight = $chairWeight;
 }

 abstract public function calcChairPrice();
 abstract public function displayChair(); 
}

class WoodChair extends Chair {
 public function calcChairPrice() {
 return $this -&gt; weight * 100;; 
 }
}

$chair = new WoodChair();
$chair -&gt; setWeight(20);
echo $chair -&gt; calcChairPrice();
?&gt;
</code></pre>

`My name is Johnny and my Roll no. is 100.`

`Johnny is saying hello.`

`My name is John and my Roll no. is 221.`

`John is saying hello.`

What is the output of the following code?
```
<?php 
interface Display{
 public function display();
}

interface Speak{
 public function speak();
}

class Student implements Display, Speak{ 
 private $name = "Johnny";
 private $rollno = "100";

 public function display(){
 echo "My name is " . $this -> name . " and my Roll no. is " . $this -> rollno . ".\n";
 }

 public function speak(){
 echo $this -> name . " is saying hello.";
 }
}

$student = new Student();
$student -> name = "John";
$student -> name = "221";
$student -> display();
$student -> speak();
?>
```

What is the output of the following code?
<pre><code>&lt;?php 
interface Display{
 public function display();
}

interface Speak{
 public function speak();
}

class Student implements Display, Speak{ 
 private $name = &quot;Johnny&quot;;
 private $rollno = &quot;100&quot;;

 public function display(){
 echo &quot;My name is &quot; . $this -&gt; name . &quot; and my Roll no. is &quot; . $this -&gt; rollno . &quot;.\n&quot;;
 }

 public function speak(){
 echo $this -&gt; name . &quot; is saying hello.&quot;;
 }
}

$student = new Student();
$student -&gt; name = &quot;John&quot;;
$student -&gt; name = &quot;221&quot;;
$student -&gt; display();
$student -&gt; speak();
?&gt;
</code></pre>

Let’s practice what we have just learned.

Let’s practice what we have just learned.

Test your understanding of abstract classes, methods, and interfaces.

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: Abstract Classes and Interfaces