PHP Object-Oriented Programming (OOP)

1. Key Concepts of OOP

There are four main concepts of OOP:

• Classes: Blueprints for creating objects. A class defines properties (attributes) and methods (functions) that the objects created from the class will have.
• Objects: Instances of classes. An object is created from a class and can hold data and perform actions defined by its class.
• Inheritance: The ability of a class to inherit properties and methods from another class. This promotes code reuse.
• Encapsulation: The bundling of data (attributes) and methods (functions) that operate on the data into a single unit (class). It restricts direct access to some of the object's components, which is a means of preventing accidental interference and misuse of the methods and data.

2. Creating a Class and Object

To create a class in PHP, use the class keyword followed by the class name. To create an object, use the new keyword.

<?php
class Car {
    // Properties
    public $color;
    public $model;

    // Method
    public function displayInfo() {
        return "Car model: " . $this->model . ", Color: " . $this->color;
    }
}

// Creating an object
$myCar = new Car();
$myCar->color = "Red";
$myCar->model = "Toyota";
echo $myCar->displayInfo(); // Output: Car model: Toyota, Color: Red
?>

3. Inheritance

Inheritance allows a class to use the properties and methods of another class. The class that inherits is called a child class, while the class it inherits from is called a parent class.

<?php
class Vehicle {
    public $brand;

    public function honk() {
        return "Beep!";
    }
}

class Car extends Vehicle {
    public function displayBrand() {
        return "Brand: " . $this->brand;
    }
}

// Creating an object of the child class
$myCar = new Car();
$myCar->brand = "Honda";
echo $myCar->displayBrand(); // Output: Brand: Honda
echo $myCar->honk(); // Output: Beep!
?>

4. Encapsulation

Encapsulation is achieved by using access modifiers: public, protected, and private.

<?php
class BankAccount {
    private $balance;

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

    public function deposit($amount) {
        $this->balance += $amount;
    }

    public function getBalance() {
        return $this->balance;
    }
}

$account = new BankAccount(100);
$account->deposit(50);
echo $account->getBalance(); // Output: 150
?>

5. Polymorphism

Polymorphism allows methods to do different things based on the object it is acting upon. It is often achieved through method overriding.

<?php
class Animal {
    public function makeSound() {
        return "Some sound";
    }
}

class Dog extends Animal {
    public function makeSound() {
        return "Woof!";
    }
}

class Cat extends Animal {
    public function makeSound() {
        return "Meow!";
    }
}

function animalSound(Animal $animal) {
    return $animal->makeSound();
}

$dog = new Dog();
$cat = new Cat();

echo animalSound($dog); // Output: Woof!
echo animalSound($cat); // Output: Meow!
?>

6. Conclusion

Object-Oriented Programming in PHP provides a powerful way to organize and structure code. By understanding classes, objects, inheritance, encapsulation, and polymorphism, you can write more maintainable and reusable code.