PHP- Object Oriented Programming

Object-oriented programming (OOP) in PHP allows you to organize your code into classes and objects, making it easier to manage and reuse. PHP supports OOP principles such as inheritance, encapsulation, and polymorphism. Here’s a comprehensive guide to OOP in PHP:

1. Classes and Objects

Defining a Class

A class is a blueprint for creating objects. It encapsulates data (properties) and behavior (methods).

php
<?php
    class Car {
        // Properties
        public $brand;
        public $color;
        
        // Constructor
        public function __construct($brand, $color) {
            $this->brand = $brand;
            $this->color = $color;
        }
        
        // Method
        public function start() {
            return "Starting the $this->color $this->brand.";
        }
    }
    ?>

Creating Objects (Instances)

Objects are instances of classes. You create objects using the new keyword.

php
<?php
    $myCar = new Car("Toyota", "Blue");
    echo $myCar->start(); // Outputs: Starting the Blue Toyota.
    ?>

2. Constructors and Destructors

Constructors

Constructors are special methods called when an object is created. They initialize object properties.

php
<?php
    class Car {
        public $brand;
        
        public function __construct($brand) {
            $this->brand = $brand;
        }
    }
    
    $myCar = new Car("Honda");
    echo $myCar->brand; // Outputs: Honda
    ?>

Destructors

Destructors are called when an object is destroyed or goes out of scope. They are useful for cleanup tasks.

php
<?php
    class Car {
        public function __destruct() {
            echo "Destroying object.";
        }
    }
    
    $myCar = new Car();
    unset($myCar); // Outputs: Destroying object.
    ?>

3. Properties and Methods

Properties

Properties are variables that hold data within objects. They can have different visibility (public, private, protected).

php
<?php
    class Car {
        public $brand; // Public property
        private $color; // Private property
        
        public function __construct($brand, $color) {
            $this->brand = $brand;
            $this->color = $color;
        }
    }
    ?>

Methods

Methods are functions defined inside a class that perform actions related to the object.

php
<?php
    class Car {
        public function start() {
            return "Starting the car.";
        }
        
        public function stop() {
            return "Stopping the car.";
        }
    }
    ?>

4. Inheritance

Inheritance allows a class (subclass) to inherit properties and methods from another class (parent class).

Parent Class

php
<?php
    class Vehicle {
        public $brand;
        
        public function __construct($brand) {
            $this->brand = $brand;
        }
        
        public function start() {
            return "Starting the $this->brand.";
        }
    }
    ?>

Subclass (Child Class)

php
<?php
    class Car extends Vehicle {
        public function __construct($brand) {
            parent::__construct($brand);
        }
        
        // Additional methods specific to Car
        public function accelerate() {
            return "Accelerating the $this->brand.";
        }
    }
    
    $myCar = new Car("Toyota");
    echo $myCar->start(); // Outputs: Starting the Toyota.
    echo $myCar->accelerate(); // Outputs: Accelerating the Toyota.
    ?>

5. Encapsulation

Encapsulation means bundling the data (properties) and methods that operate on the data into a single unit (class). It helps in hiding the internal state of objects and restricting direct access to certain components.

php
<?php
    class BankAccount {
        private $balance;
        
        public function __construct($balance) {
            $this->balance = $balance;
        }
        
        public function deposit($amount) {
            $this->balance += $amount;
        }
        
        public function withdraw($amount) {
            if ($amount <= $this->balance) {
                $this->balance -= $amount;
            } else {
                echo "Insufficient funds.";
            }
        }
        
        public function getBalance() {
            return $this->balance;
        }
    }
    
    $account = new BankAccount(1000);
    $account->deposit(500);
    echo $account->getBalance(); // Outputs: 1500
    $account->withdraw(2000); // Outputs: Insufficient funds.
    ?>

6. Polymorphism

Polymorphism allows objects of different classes to be treated as objects of a common superclass. It allows flexibility in method implementation.

Example

php
<?php
    interface Shape {
        public function area();
    }
    
    class Circle implements Shape {
        private $radius;
        
        public function __construct($radius) {
            $this->radius = $radius;
        }
        
        public function area() {
            return pi() * $this->radius * $this->radius;
        }
    }
    
    class Rectangle implements Shape {
        private $width;
        private $height;
        
        public function __construct($width, $height) {
            $this->width = $width;
            $this->height = $height;
        }
        
        public function area() {
            return $this->width * $this->height;
        }
    }
    
    $shapes = [
        new Circle(5),
        new Rectangle(3, 4)
    ];
    
    foreach ($shapes as $shape) {
        echo "Area: " . $shape->area() . "<br>";
    }
    ?>

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