Introduction to OOP in PHP

Object-Oriented Programming (OOP) is a programming style that organizes code into objects, which are created from classes. PHP supports OOP concepts that help developers build scalable, reusable, and maintainable applications.

In real-world PHP development—especially in frameworks like Laravel, WordPress plugins, or large DevOps tools—OOP is heavily used to structure code efficiently.

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What is a Class in PHP?

class Car {
    public $brand;
    public $color;

    public function startEngine() {
        echo "Engine Started";
    }

A class is a blueprint or template used to create objects.

It defines:

• Properties (variables)
• Methods (functions)

Think of a class as:

Blueprint → Object = Real Product

Example:

class Car {
    public $brand;
    public $color;

    public function startEngine() {
        echo "Engine Started";
    }
}

Here:

• Car → Class
• $brand, $color → Properties
• startEngine() → Method

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What is an Object in PHP?

An object is an instance of a class.

It represents a real-world entity created from a class blueprint.

Example:

$car1 = new Car();
$car1->brand = "Toyota";
$car1->color = "Red";

$car1->startEngine();

Output:

Engine Started

Here:

• $car1 → Object
• new → Creates object
• -> → Access properties/methods

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Basic Class and Object Example

<?php

class Student {

    public $name;
    public $age;

    public function showDetails() {
        echo "Name: " . $this->name;
        echo "<br>";
        echo "Age: " . $this->age;
    }
}

$student1 = new Student();

$student1->name = "Raj";
$student1->age = 25;

$student1->showDetails();

?>

Output:

Name: Raj
Age: 25

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Understanding $this Keyword

$this refers to the current object.

Used to access:

• Properties
• Methods inside class

Example:

class Employee {

    public $salary;

    public function setSalary($amount) {
        $this->salary = $amount;
    }

    public function getSalary() {
        return $this->salary;
    }
}

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Constructor in PHP

A constructor automatically runs when an object is created.

Constructor method:

__construct()

Example:

class Laptop {

    public $brand;
    public $price;

    public function __construct($brand, $price) {
        $this->brand = $brand;
        $this->price = $price;
    }

    public function showLaptop() {
        echo $this->brand . " costs " . $this->price;
    }
}

$l1 = new Laptop("Apple", 2000);
$l1->showLaptop();

Output:

Apple costs 2000

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Destructor in PHP

Destructor runs when object is destroyed.

__destruct()

Example:

class Test {

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

$t = new Test();

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Access Modifiers (Visibility)

Access modifiers control access to properties and methods.

Three types:

1. Public
2. Private
3. Protected

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Public

Accessible anywhere.

class User {

    public $username;

    public function show() {
        echo $this->username;
    }
}

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Private

Accessible only inside class.

class Bank {

    private $balance = 1000;

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

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Protected

Accessible inside class and child classes.

class ParentClass {

    protected $value = 50;
}

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Creating Multiple Objects

You can create many objects from one class.

class Animal {

    public $name;

    public function speak() {
        echo $this->name . " makes sound";
    }
}

$a1 = new Animal();
$a1->name = "Dog";

$a2 = new Animal();
$a2->name = "Cat";

$a1->speak();
echo "<br>";
$a2->speak();

Output:

Dog makes sound
Cat makes sound

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Class Methods

Methods are functions inside classes.

Example:

class Calculator {

    public function add($a, $b) {
        return $a + $b;
    }
}

$calc = new Calculator();

echo $calc->add(5, 10);

Output:

15

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Static Properties and Methods

Static members belong to class, not objects.

Use:

static

Access using:

ClassName::$property
ClassName::method()

Example:

class Counter {

    public static $count = 0;

    public static function increment() {
        self::$count++;
    }
}

Counter::increment();

echo Counter::$count;

Output:

1

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Constants in Class

Defined using:

const

Example:

class Math {

    const PI = 3.14;
}

echo Math::PI;

Output:

3.14

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Real-World Example — User Management

class User {

    public $name;
    public $email;

    public function __construct($name, $email) {

        $this->name = $name;
        $this->email = $email;
    }

    public function showUser() {

        echo "Name: " . $this->name;
        echo "<br>";
        echo "Email: " . $this->email;
    }
}

$user1 = new User(
    "Raj",
    "raj@example.com"
);

$user1->showUser();

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Real-World Example — Product System

class Product {

    public $name;
    public $price;

    public function __construct($name, $price) {

        $this->name = $name;
        $this->price = $price;
    }

    public function getDiscountPrice($percent) {

        $discount =
            $this->price * $percent / 100;

        return $this->price - $discount;
    }
}

$p1 = new Product(
    "Laptop",
    1000
);

echo $p1->getDiscountPrice(10);

Output:

900

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Difference Between Class and Object

Feature	Class	Object
Definition	Blueprint	Instance
Memory	No memory	Uses memory
Purpose	Define structure	Represent real entity
Example	Car	Toyota Car

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Advantages of Using Classes & Objects

• Code reusability
• Better organization
• Easy maintenance
• Scalability
• Real-world modeling
• Security via encapsulation

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Best Practices for PHP Classes

Follow these:

1. Use meaningful class names

Example:

class OrderManager

Not:

class Test

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2. Keep classes focused (Single Responsibility)

Bad:

class User {
    // login
    // payment
    // report
}

Good:

class User
class Payment
class Report

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3. Use constructor initialization

Good:

public function __construct($name)

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4. Use private properties with getters/setters

private $balance;

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

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Common Mistakes Beginners Make

Avoid:

Missing $this

Wrong:

name = $name;

Correct:

$this->name = $name;

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Forgetting new

Wrong:

$car = Car();

Correct:

$car = new Car();

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Accessing private properties directly

Wrong:

$obj->balance;

Correct:

$obj->getBalance();

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Practice Exercises

Try these.

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Exercise 1 — Create a Book Class

Requirements:

• Properties: title, author
• Method: showBook()

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Exercise 2 — Create Employee Class

Requirements:

• Constructor
• Salary calculation method

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Exercise 3 — Static Counter

Requirements:

• Count number of objects created

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Interview Questions (Important)

Q1: What is a class?
A class is a blueprint used to create objects.

Q2: What is an object?
An object is an instance of a class.

Q3: What is $this?
It refers to current object.

Q4: What is constructor?
A method that runs automatically when object is created.

Q5: Difference between class and object?
Class defines structure; object represents real entity.

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Summary

In this tutorial you learned:

• What is a class
• What is an object
• How to create objects
• Constructors and destructors
• Access modifiers
• Static members
• Constants
• Real-world examples
• Best practices

Class and Object are the foundation of PHP OOP. Once you understand them well, you can easily learn:

• Inheritance
• Polymorphism
• Encapsulation
• Abstraction
• Interfaces
• Traits

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Next Recommended Tutorial

After Class & Object, learn:

1. Inheritance in PHP
2. Encapsulation
3. Polymorphism
4. Abstraction
5. Interfaces
6. Traits

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