OOP in PHP helps you write modular, reusable, and maintainable code by organizing it into objects.

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🔹 1. Classes & Objects

✅ Class

A class is a blueprint/template for creating objects.

class Car {
    public $name;    public function start() {
        echo "Car started";
    }
}

✅ Object

An object is an instance of a class.

$car1 = new Car();
$car1->name = "BMW";
$car1->start();

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🔹 2. Properties & Methods

• Properties → Variables inside a class
• Methods → Functions inside a class

class Student {
    public $name;    public function showName() {
        echo $this->name;
    }
}

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🔹 3. Constructor & Destructor

✅ Constructor (__construct)

Runs automatically when object is created

class User {
    public function __construct() {
        echo "Object Created";
    }
}

✅ Destructor (__destruct)

Runs when object is destroyed

class User {
    public function __destruct() {
        echo "Object Destroyed";
    }
}

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🔹 4. Inheritance

Allows one class to inherit properties & methods from another class.

class Animal {
    public function sound() {
        echo "Animal sound";
    }
}class Dog extends Animal {
    public function bark() {
        echo "Bark";
    }
}

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🔹 5. Encapsulation

Wrapping data and restricting access using access modifiers.

Access Modifiers:

• public → accessible everywhere
• private → only inside class
• protected → class + inherited classes

class Bank {
    private $balance = 1000;    public function getBalance() {
        return $this->balance;
    }
}

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🔹 6. Polymorphism

Same function name, different behavior.

class Animal {
    public function sound() {
        echo "Animal sound";
    }
}class Cat extends Animal {
    public function sound() {
        echo "Meow";
    }
}

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🔹 7. Traits

Traits allow code reuse (like multiple inheritance workaround).

trait Logger {
    public function log($msg) {
        echo $msg;
    }
}class User {
    use Logger;
}

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🔹 8. Interfaces & Abstract Classes

✅ Interface

Only method declarations (no body)

interface Payment {
    public function pay($amount);
}

✅ Abstract Class

Can have both abstract and normal methods

abstract class Shape {
    abstract public function area();
}

Example:

class Circle extends Shape {
    public function area() {
        return 3.14 * 10 * 10;
    }
}

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🚀 Pro Tips (Important for Students)

✔ Use OOP for large projects
✔ Follow SOLID principles (advanced)
✔ Practice with real examples:

• User login system
• Blog system
• E-commerce cart