PHP Class & Object

PHP, like many other programming languages, supports object-oriented programming (OOP). In OOP, a class is a blueprint for creating objects (a particular data structure), providing initial values for state (member variables or properties), and implementations of behavior (member functions or methods).

Class

A class is defined with the class keyword followed by the class name. Inside the class, you can define properties and methods.

Object

An object is an instance of a class. Once you have a class, you can create objects from that class.

Example: Defining a Class and Creating an Object

Let's go through a simple example to demonstrate how to define a class and create objects in PHP.

Step 1: Define a Class

<?php
class Car {
    // Properties
    public $make;
    public $model;
    public $year;
    
    // Constructor
    public function __construct($make, $model, $year) {
        $this->make = $make;
        $this->model = $model;
        $this->year = $year;
    }
    
    // Methods
    public function getCarDetails() {
        return "This car is a $this->year $this->make $this->model.";
    }
}
?>

Step 2: Create Objects from the Class

<?php
// Include the class definition
include 'Car.php';

// Create an object of the class Car
$myCar = new Car("Toyota", "Corolla", 2020);
$anotherCar = new Car("Honda", "Civic", 2019);

// Access properties and methods
echo $myCar->getCarDetails(); // Output: This car is a 2020 Toyota Corolla.
echo $anotherCar->getCarDetails(); // Output: This car is a 2019 Honda Civic.
?>

Explanation

  1. Class Definition:

    • class Car { ... }: Defines a class named Car.
    • Properties: Variables defined inside a class are called properties. In this example, $make, $model, and $year are properties of the Car class.
    • Constructor: The __construct method is a special method called when an object is instantiated. It initializes the properties of the class.
    • Methods: Functions defined inside a class are called methods. In this example, getCarDetails() is a method that returns a string describing the car.

  2. Creating Objects:

    • new Car("Toyota", "Corolla", 2020): Creates a new object of the Car class and passes parameters to the constructor.
    • echo $myCar->getCarDetails();: Calls the getCarDetails() method on the $myCar object, which outputs the details of the car.

Access Modifiers

In PHP, properties and methods can have access modifiers to define their visibility:

  • public: Accessible from anywhere.
  • protected: Accessible within the class and by inheriting classes.
  • private: Accessible only within the class itself.

Example with Access Modifiers

<?php
class Car {
    // Properties
    private $make;
    private $model;
    private $year;
    
    // Constructor
    public function __construct($make, $model, $year) {
        $this->make = $make;
        $this->model = $model;
        $this->year = $year;
    }
    
    // Methods
    public function getCarDetails() {
        return "This car is a $this->year $this->make $this->model.";
    }
    
    public function setYear($year) {
        if($year > 1885 && $year <= date("Y")) {
            $this->year = $year;
        } else {
            echo "Invalid year.";
        }
    }
}
?>

In this example:

  • The properties $make, $model, and $year are private, meaning they can't be accessed directly from outside the class.
  • The setYear method is used to set the year property with validation.

Creating and Using the Object

<?php
$myCar = new Car("Toyota", "Corolla", 2020);
echo $myCar->getCarDetails(); // Output: This car is a 2020 Toyota Corolla.

$myCar->setYear(2022);
echo $myCar->getCarDetails(); // Output: This car is a 2022 Toyota Corolla.

$myCar->setYear(1800); // Output: Invalid year.
?>

This illustrates the basics of using classes and objects in PHP. By following these principles, you can build more complex and organized applications.



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