PHP What is OOP

Introduction to Object-Oriented Programming (OOP vs Procedural)

Object-Oriented Programming (OOP) is a programming paradigm based on the concept of "objects" containing data (properties) and code (methods). OOP organizes software design around data structures rather than standalone procedural functions.

Procedural vs Object-Oriented Programming

The 4 Pillars of OOP

flowchart TD
    A["4 Pillars of OOP"] --> B["1. Encapsulation"]
    A --> C["2. Abstraction"]
    A --> D["3. Inheritance"]
    A --> E["4. Polymorphism"]
    B --> B1["Bundling data & restricting direct property access"]
    C --> C1["Hiding internal complexity behind simple interfaces"]
    D --> D1["Reusing parent class features in child classes"]
    E --> E1["Objects of different classes sharing identical method signatures"]

Practical Code Example

<?php
declare(strict_types=1);

// Encapsulated Class Definition
class UserAccount
{
    // Encapsulated Private Properties
    private string $email;
    private bool $isActive = true;

    public function __construct(string $email)
    {
        $this->setEmail($email);
    }

    // Getter Method
    public function getEmail(): string
    {
        return $this->email;
    }

    // Setter Method with Validation
    public function setEmail(string $email): void
    {
        if (!filter_var($email, FILTER_VALIDATE_EMAIL)) {
            throw new InvalidArgumentException("Invalid email format.");
        }
        $this->email = $email;
    }
}

// Instantiating Object
$user = new UserAccount("[email protected]");
echo "Encapsulated User Email: " . $user->getEmail() . "
";

Best Practices

• Group Related State and Behavior: Keep methods inside the class that owns the target state properties.
• Favor Encapsulation: Keep class properties private or protected and expose public getter/setter methods.
• Design for Single Responsibility: Each class should have one clear responsibility in the application.

Self-Check Challenge

Name the 4 core pillars of Object-Oriented Programming! (Encapsulation, Abstraction, Inheritance, Polymorphism)