Chapter 9: Object-Oriented Programming in PHP

In this chapter, we will explore object-oriented programming (OOP) in PHP. We will cover the principles of OOP, creating classes and objects, defining properties and methods, inheritance, and encapsulation.

9.1 Introduction to object-oriented programming:

Object-oriented programming is a programming paradigm that focuses on creating objects that encapsulate data and behavior.

OOP principles include encapsulation, inheritance, and polymorphism.

9.2 Creating classes and objects:

Classes are blueprints for creating objects, defining their properties and methods.

Objects are instances of classes, representing individual entities in the application.

Example:

php

""

<?php

   // Class definition

   class Car {

       // Properties

       public $brand;

       public $color;

       

       // Methods

       public function startEngine() {

           echo "Engine started!";

       }

   }

   

   // Object instantiation

   $myCar = new Car();

   $myCar->brand = "Toyota";

   $myCar->color = "Red";

   

   // Accessing object properties and methods

   echo $myCar->brand; // Output: Toyota

   $myCar->startEngine(); // Output: Engine started!

?>

9.3 Defining properties and methods:

Properties represent the state or characteristics of an object.

Methods are functions defined within a class, representing the behavior or actions that objects can perform.

Example:

php

""

<?php

   class Circle {

       // Property

       public $radius;

       

       // Method to calculate area

       public function calculateArea() {

           return 3.14 * $this->radius * $this->radius;

       }

   }

   

   // Object instantiation

   $myCircle = new Circle();

   $myCircle->radius = 5;

   

   // Accessing object properties and methods

   echo $myCircle->calculateArea(); // Output: 78.5

?>

9.4 Inheritance:

Inheritance allows classes to inherit properties and methods from other classes.

The child class extends the parent class, inheriting its features and can also add new properties and methods.

Example:

php

""

<?php

   // Parent class

   class Animal {

       public function eat() {

           echo "Eating...";

       }

   }

   

   // Child class inheriting from Animal

   class Dog extends Animal {

       public function bark() {

           echo "Woof!";

       }

   }

   

   // Creating an instance of the child class

   $myDog = new Dog();

   

   // Accessing inherited method

   $myDog->eat(); // Output: Eating...

   

   // Accessing child class method

   $myDog->bark(); // Output: Woof!

?>

9.5 Encapsulation:

Encapsulation refers to the bundling of data and methods within a class, hiding internal details from the outside world.

Access modifiers like public, protected, and private control the visibility and accessibility of properties and methods.

Example:

php

""

<?php

   class Person {

       // Public property

       public $name;

       

       // Private property

       private $age;

       

       // Public method

       public function greet() {

           echo "Hello, my name is " . $this->name;

       }

       

       // Private method

       private function getAge() {

           return $this->age;

       }

   }

   

   $person = new Person();

   $person->name = "John";

   $person->greet(); // Output: Hello, my name is John

?>

By following the explanations and examples in this chapter, you will gain a solid understanding of object-oriented programming in PHP, allowing you to create classes and objects, define properties and methods, implement inheritance, and utilize encapsulation to build modular and maintainable applications.