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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

Methods that serve the same functionality in different classes should have the same
name.

Polymorphism is the Greek term for inheritance.

Polymorphism can be implemented in most modern programming languages.

Which sentence best defines the polymorphism principle in PHP?


Which sentence best defines the polymorphism principle in PHP?

**(Fill in the blank)** Polymorphism principle can be implemented with ________.


(Fill in the blank) Polymorphism principle can be implemented with ________.

Scalar types (booleans, integers, floats, and strings) are supported in PHP 5 but not in PHP 7.

Complex types (arrays, objects, and interfaces) are supported in PHP 7 only. 

Type hinting for complex types (arrays and objects) is supported in both PHP 5 and 7, while scalar type hinting (for integers, floats, strings, and booleans) is only supported in PHP 7.


Which data types can be declared with type hinting?

Which data types can be declared with type hinting?

`John of age 25 says Hello.`

`Johnny of age 30 says Hi.`

What is the output of the following code?

```
<?php
interface Person{
 public function greet();
}

class John implements Person{ 
 private $age;

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

 public function greet(){
 echo "John of age " . $this -> age . " says Hello.\n";
 }
}

class Johnny implements Person{ 
 private $age;

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

 public function greet(){
 echo "Johnny of age " . $this -> age . " says Hi.\n";
 }
}

$person1 = new John(25);
$person1 = new Johnny(30);
echo $person1 -> greet();
?>
```

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

class John implements Person{ 
 private $age;

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

 public function greet(){
 echo &quot;John of age &quot; . $this -&gt; age . &quot; says Hello.\n&quot;;
 }
}

class Johnny implements Person{ 
 private $age;

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

 public function greet(){
 echo &quot;Johnny of age &quot; . $this -&gt; age . &quot; says Hi.\n&quot;;
 }
}

$person1 = new John(25);
$person1 = new Johnny(30);
echo $person1 -&gt; greet();
?&gt;
</code></pre>

What is the output of the following code?
```
<?php 
 
 class Test{ 
 private $greeting = "Hello."; 
 private $message = " Just checking type hinting.";
 } 

 function typehint(Test $t1){ 
 echo $t1 -> greeting . $t1 -> message; 
 } 

 typehint(new Test()); 
?> 
```

What is the output of the following code?
<pre><code>&lt;?php 
 
 class Test{ 
 private $greeting = &quot;Hello.&quot;; 
 private $message = &quot; Just checking type hinting.&quot;;
 } 

 function typehint(Test $t1){ 
 echo $t1 -&gt; greeting . $t1 -&gt; message; 
 } 

 typehint(new Test()); 
?&gt; 
</code></pre>

`Cat moves on 4 legs`

`Cat eats food`

`All animals eat`


`Cat moves on 4 legs`

`Cat eats food`

`Cat eats food`


`Cat moves on 4 legs`

`All animals eat`

`All animals eat`


The `Dog` class cannot call the `eat()` method since the parent class doesn’t contain the `eat()` method.


What is the output of the code below?
```
<?php
abstract class Traits{
 public function eat(){
 echo "All animals eat\n";
 }
 abstract public function move();
}

class Animal extends Traits{ 
 public function move(){
 echo "All animals move\n";
 }
}
class Cat extends Animal {
 public function move() {
 echo "Cat moves on 4 legs\n";
 }
 public function eat() {
 echo "Cat eats food\n";
 }
}
class Dog extends Animal {
 public function move() {
 echo "Dog moves on 4 legs\n";
 }
 public function eat() {
 parent:: eat();
 }
}

$animal = new Cat(); 
$animal -> move();
$animal -> eat();
$animal = new Dog();
$animal -> eat();
?>
```

What is the output of the code below?
<pre><code>&lt;?php
abstract class Traits{
 public function eat(){
 echo &quot;All animals eat\n&quot;;
 }
 abstract public function move();
}

class Animal extends Traits{ 
 public function move(){
 echo &quot;All animals move\n&quot;;
 }
}
class Cat extends Animal {
 public function move() {
 echo &quot;Cat moves on 4 legs\n&quot;;
 }
 public function eat() {
 echo &quot;Cat eats food\n&quot;;
 }
}
class Dog extends Animal {
 public function move() {
 echo &quot;Dog moves on 4 legs\n&quot;;
 }
 public function eat() {
 parent:: eat();
 }
}

$animal = new Cat(); 
$animal -&gt; move();
$animal -&gt; eat();
$animal = new Dog();
$animal -&gt; eat();
?&gt;
</code></pre>

Let’s practice what we have just learned.

Let’s practice what we have just learned.

A short quiz to test your understanding of the polymorphism principle and type hinting.

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: Polymorphism & Type Hinting