Object-Oriented PHP 🏗️

Organise your code with classes, objects, inheritance, interfaces, and PHP 8's constructor promotion — the foundation of modern PHP.

What You'll Learn in This Lesson

• Classes, objects, constructors, and the $this keyword
• Access modifiers: public, protected, private
• Inheritance with extends and parent::
• Interfaces and abstract classes
• PHP 8 constructor promotion for cleaner code

Note: PHP runs on a server. Our examples simulate PHP logic using JavaScript. To run real PHP, install PHP.

🎯 Real-World Analogy: A class is like an architectural blueprint — it defines what a house (object) will look like. You can build many houses from the same blueprint. Inheritance is like a "luxury house" blueprint that extends the basic house with extra features. An interface is like a building code — it says "every house MUST have a fire exit" but doesn't specify how to build one.

Try It: Classes & Objects

Create classes with constructors, methods, static methods, and access modifiers

Try it Yourself »

JavaScript

// PHP OOP: Classes & Objects (simulated in JavaScript)
console.log("=== Classes: The Blueprint ===");
console.log();

// PHP class with constructor, properties, methods
class User {
    // In PHP: private string $name; private string $email;
    constructor(name, email, role = "user") {
        this.name = name;      // PHP: $this->name = $name;
        this.email = email;
        this.role = role;
        this.createdAt = new Date().toISOString().slice(0, 10);
    }

    getInfo() {
        re
...

Try It: Inheritance & Interfaces

Extend classes, implement interfaces, and use PHP 8 constructor promotion

Try it Yourself »

JavaScript

// PHP OOP: Inheritance, Interfaces & Abstract Classes
console.log("=== Inheritance (extends) ===");
console.log();

class Animal {
    constructor(name, sound) {
        this.name = name;
        this.sound = sound;
    }
    speak() { return this.name + " says " + this.sound + "!"; }
    toString() { return "[Animal: " + this.name + "]"; }
}

class Dog extends Animal {
    constructor(name, breed) {
        super(name, "Woof");  // PHP: parent::__construct($name, "Woof");
        this.breed = 
...

⚠️ Common Mistakes

⚠️

Making everything public — use private for properties and expose through getters/setters. This prevents external code from putting objects in invalid states.

⚠️

Deep inheritance chains — more than 2-3 levels deep becomes hard to maintain. Prefer composition (having objects) over inheritance (being objects).

⚠️

Forgetting parent::__construct() — child classes must call the parent constructor if the parent has one.

💡

Pro Tip: Use PHP 8's constructor promotion — it reduces boilerplate by 60% and makes classes much more readable.

📋 Quick Reference — OOP

Concept	Keyword	Purpose
Class	class Foo {}	Define a blueprint
Object	new Foo()	Create an instance
Inherit	extends	Build on existing class
Interface	implements	Enforce a contract
Abstract	abstract class	Base class (can't instantiate)
Static	Class::method()	Call without object

🎉 Lesson Complete!

You've mastered Object-Oriented PHP! Next, learn how to connect your PHP app to a MySQL database.