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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

To group related classes, interfaces, functions, and constants

Which keyword is used to define a namespace?


Which keyword is used to define a namespace?

Which keyword is used to import a namespace?

Which keyword is used to import a namespace?

We define a `Acme\Book` namespace in a `BookIntro.php` file in the `src/Book` directory.

```
<?php 
namespace Acme\Book;

class BookIntro {
 public function sayHello() {
 return "Hello!"; 
 }

 protected function myTitle()
 {
 return "I am a PHP book"; 
 }
}
?>
```
We use the above namespace in the following code file.

```
<?php 
require "src/Book/BookIntro.php";

use Acme\Book\BookIntro as Book;


$book = new Book(); 
echo $book -> sayHello(). " " . $book -> myTitle();
?>
``` 
What is the output of the above code?

We define a <code>Acme\Book</code> namespace in a <code>BookIntro.php</code> file in the <code>src/Book</code> directory.
<pre><code>&lt;?php 
namespace Acme\Book;

class BookIntro {
 public function sayHello() {
 return &quot;Hello!&quot;; 
 }

 protected function myTitle()
 {
 return &quot;I am a PHP book&quot;; 
 }
}
?&gt;
</code></pre>
We use the above namespace in the following code file.
<pre><code>&lt;?php 
require &quot;src/Book/BookIntro.php&quot;;

use Acme\Book\BookIntro as Book;


$book = new Book(); 
echo $book -&gt; sayHello(). &quot; &quot; . $book -&gt; myTitle();
?&gt;
</code></pre>
What is the output of the above code?

What is the output of the following code?
```
<?php 
class HumanDriver {
 public function whoAmI() {
 return "I am human."; 
 }
}
class RobotDriver {
 public function whoAmI() {
 return "I am robot."; 
 }
}
class Car {
 protected $driver;

 public function __construct($driver) {
 $this -> driver = $driver;
 }

 public function getDriver(){
 return $this -> driver; 
 }
}

$driver = new HumanDriver();
$car = new Car($driver);
$driver = new RobotDriver(); 
$Car = new Car($driver);
echo $car -> getDriver();
echo $Car -> getDriver();
?>
```

What is the output of the following code?
<pre><code>&lt;?php 
class HumanDriver {
 public function whoAmI() {
 return &quot;I am human.&quot;; 
 }
}
class RobotDriver {
 public function whoAmI() {
 return &quot;I am robot.&quot;; 
 }
}
class Car {
 protected $driver;

 public function __construct($driver) {
 $this -&gt; driver = $driver;
 }

 public function getDriver(){
 return $this -&gt; driver; 
 }
}

$driver = new HumanDriver();
$car = new Car($driver);
$driver = new RobotDriver(); 
$Car = new Car($driver);
echo $car -&gt; getDriver();
echo $Car -&gt; getDriver();
?&gt;
</code></pre>

`Hello! I am a PHP book`

`Hello! I am a Python book`

We define a `Acme\Book` namespace in `PhpIntro.php` and `PythonIntro.php` in the `src/Book` directory. The `PhpIntro.php` file is as follows:
```
<?php 
namespace Acme\Book;

class PhpIntro {
 public function sayHello() {
 return "Hello!"; 
 }

 public function myTitle()
 {
 return "I am a PHP book"; 
 }
}
?>
```
Here is the code for the `PythonIntro.php` file.
```
<?php 
namespace Acme\Book;

class PythonIntro {
 public function sayHello() {
 return "Hello!"; 
 }

 public function myTitle()
 {
 return "I am a Python book"; 
 }
}
?>
```
We use the above namespaces in the following code file:

```
<?php 
require "src/Book/PhpIntro.php";
require "src/Book/PythonIntro.php";

use Acme\Book\PhpIntro as Php;
use Acme\{
Book\PythonIntro as Python 
};


$php = new Php(); 
$python = new Python(); 
echo $php -> sayHello(). " " . $php -> myTitle() . "\n";
echo $python -> sayHello(). " " . $python -> myTitle();
?>
``` 
What is the output of the above code?

We define a <code>Acme\Book</code> namespace in <code>PhpIntro.php</code> and <code>PythonIntro.php</code> in the <code>src/Book</code> directory. The <code>PhpIntro.php</code> file is as follows:
<pre><code>&lt;?php 
namespace Acme\Book;

class PhpIntro {
 public function sayHello() {
 return &quot;Hello!&quot;; 
 }

 public function myTitle()
 {
 return &quot;I am a PHP book&quot;; 
 }
}
?&gt;
</code></pre>
Here is the code for the <code>PythonIntro.php</code> file.
<pre><code>&lt;?php 
namespace Acme\Book;

class PythonIntro {
 public function sayHello() {
 return &quot;Hello!&quot;; 
 }

 public function myTitle()
 {
 return &quot;I am a Python book&quot;; 
 }
}
?&gt;
</code></pre>
We use the above namespaces in the following code file:
<pre><code>&lt;?php 
require &quot;src/Book/PhpIntro.php&quot;;
require &quot;src/Book/PythonIntro.php&quot;;

use Acme\Book\PhpIntro as Php;
use Acme\{
Book\PythonIntro as Python 
};


$php = new Php(); 
$python = new Python(); 
echo $php -&gt; sayHello(). &quot; &quot; . $php -&gt; myTitle() . &quot;\n&quot;;
echo $python -&gt; sayHello(). &quot; &quot; . $python -&gt; myTitle();
?&gt;
</code></pre>
What is the output of the above code?

`Fatal error: RobotDriver class doesn’t implement Driver interface`

What is the output of the following code?
```
<?php 
interface Driver
{
 public function whoAmI();
}
class HumanDriver implements Driver{
 public function whoAmI() {
 return "I am human."; 
 }
}
class RobotDriver{
 public function whoAmI() {
 return "I am robot."; 
 }
}
class Car {
 protected $driver;

 public function __construct(Driver $driver) {
 $this -> driver = $driver;
 }

 public function getDriver(){
 return $this -> driver; 
 }
}

$driver = new HumanDriver();
$car = new Car($driver);
echo $car -> getDriver() ->whoAmI();
$driver = new RobotDriver();
echo $car -> getDriver() ->whoAmI();
?>

```

What is the output of the following code?
<pre><code>&lt;?php 
interface Driver
{
 public function whoAmI();
}
class HumanDriver implements Driver{
 public function whoAmI() {
 return &quot;I am human.&quot;; 
 }
}
class RobotDriver{
 public function whoAmI() {
 return &quot;I am robot.&quot;; 
 }
}
class Car {
 protected $driver;

 public function __construct(Driver $driver) {
 $this -&gt; driver = $driver;
 }

 public function getDriver(){
 return $this -&gt; driver; 
 }
}

$driver = new HumanDriver();
$car = new Car($driver);
echo $car -&gt; getDriver() -&gt;whoAmI();
$driver = new RobotDriver();
echo $car -&gt; getDriver() -&gt;whoAmI();
?&gt;

</code></pre>

Test your understanding of namespaces and dependency injection.


Quiz: Namespaces & Dependency Injection

Test your understanding of namespaces and dependency injection.

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: Namespaces