Introduction to Object-Oriented PHP (OOP)

What is Object-Oriented Programming in PHP?

Object-Oriented Programming (OOP) is a programming paradigm based on the concept of “objects”, which bundle data (properties) and functions (methods) into single reusable structures.

Instead of writing procedural code in a top-to-bottom sequence, OOP lets you model real-world entities and reuse code more efficiently.

Benefits of OOP:

• Better code organization and structure
• Encourages modularity and reusability
• Easier to maintain and scale large applications
• Common in PHP frameworks like Laravel, Symfony, and CodeIgniter

Basic Structure of a PHP Class

Defining a Class:

class Car {
  public $brand = "Toyota";

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

class Car {
  public $brand = "Toyota";

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

Creating an Object:

$myCar = new Car();
echo $myCar->brand;       // Output: Toyota
echo $myCar->honk();      // Output: Beep!

$myCar = new Car();
echo $myCar->brand;       // Output: Toyota
echo $myCar->honk();      // Output: Beep!

A class is like a blueprint, and an object is a real instance created from it.

Properties and Methods

• Properties are variables inside a class
• Methods are functions defined inside a class

Example:

class Person {
  public $name;
  
  public function sayHello() {
    return "Hello, my name is " . $this->name;
  }
}

class Person {
  public $name;
  
  public function sayHello() {
    return "Hello, my name is " . $this->name;
  }
}

$user = new Person();
$user->name = "Emma";
echo $user->sayHello(); // Output: Hello, my name is Emma

$user = new Person();
$user->name = "Emma";
echo $user->sayHello(); // Output: Hello, my name is Emma

$this refers to the current object inside the class.

Constructors and Destructors

Constructor:

Runs automatically when an object is created. Used to initialize values.

class User {
  public $name;

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

class User {
  public $name;

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

$user1 = new User("Jay");
echo $user1->name; // Output: Jay

$user1 = new User("Jay");
echo $user1->name; // Output: Jay

Destructor:

Runs when the object is destroyed (end of script or manually unset).

public function __destruct() {
  echo "Object destroyed.";
}

public function __destruct() {
  echo "Object destroyed.";
}

Access Modifiers: public, private, protected

They control visibility of properties and methods:

Example:

class BankAccount {
  private $balance = 1000;

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

class BankAccount {
  private $balance = 1000;

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

$acc = new BankAccount();
// echo $acc->balance; ❌ Error: private property
echo $acc->getBalance(); // ✅ Output: 1000

$acc = new BankAccount();
// echo $acc->balance; ❌ Error: private property
echo $acc->getBalance(); // ✅ Output: 1000

Real-World Example: Simple Calculator Class

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

  public function subtract($a, $b) {
    return $a - $b;
  }
}

$calc = new Calculator();
echo $calc->add(10, 5);       // Output: 15
echo $calc->subtract(10, 5);  // Output: 5

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

  public function subtract($a, $b) {
    return $a - $b;
  }
}

$calc = new Calculator();
echo $calc->add(10, 5);       // Output: 15
echo $calc->subtract(10, 5);  // Output: 5

Example: User Profile Object

class User {
  public $name;
  public $email;

  public function __construct($name, $email) {
    $this->name = $name;
    $this->email = $email;
  }

  public function getProfile() {
    return "Name: $this->name | Email: $this->email";
  }
}

$user1 = new User("Emma", "emma@example.com");
echo $user1->getProfile();

class User {
  public $name;
  public $email;

  public function __construct($name, $email) {
    $this->name = $name;
    $this->email = $email;
  }

  public function getProfile() {
    return "Name: $this->name | Email: $this->email";
  }
}

$user1 = new User("Emma", "emma@example.com");
echo $user1->getProfile();

Common Mistakes to Avoid

• Forgetting to use $this-> inside methods
• Directly accessing private or protected properties from outside the class
• Not using constructors to initialize required properties
• Mixing procedural and object-oriented code without structure

Best Practices for OOP in PHP

• Use camelCase for property and method names
• Keep properties private or protected, expose via getter/setter
• Use constructors to enforce necessary values
• Keep each class focused on one purpose (Single Responsibility Principle)
• Favor composition over inheritance (covered later)

Notes:

• Object-Oriented PHP helps build scalable, modular, and maintainable code
• Classes define blueprints; objects are real instances
• Use constructors to initialize objects and access modifiers to protect data
• OOP is the foundation of modern PHP frameworks and applications

Practice Tasks

Task 1: Book Class
Create a Book class with:

• Properties: title, author
• Constructor to initialize both
• Method to return formatted string: “Title by Author”

Task 2: BankAccount Class

• Private property balance
• Public method deposit($amount) and getBalance()

Task 3: Auto Profile Generator
Create a Profile class that takes name, age, and location and displays:
Jay is 30 years old and lives in Mumbai.