OOP — Access Modifiers, Inheritance & Constants

public — accessible everywhere. protected — class + child classes. private — only inside the same class.

Access Modifiers

public — accessible everywhere. protected — class + child classes. private — only inside the same class.

Real-life example: public is a shop window. protected is staff-only back room. private is the owner's safe.

public, protected, private

<?php
class Account {
  public string $username = "asha";
  protected float $balance = 1000.0;
  private string $pin = "1234";
}

$acc = new Account();
echo $acc->username;
// echo $acc->balance; // Error — protected
?>

Inheritance

A child class extends a parent with extends ParentClass. It inherits methods and can override them.

Real-life example: Inheritance is a family recipe — the child adds new spices but keeps the base dish.

extends and override

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

class Dog extends Animal {
  public function speak(): string {
    return "Woof!";
  }
}

$dog = new Dog();
echo $dog->speak();
?>

Class Constants

Define constants inside a class with const NAME = value. Access with ClassName::NAME or self::NAME inside the class.

Real-life example: Class constants are the company logo color — same everywhere, never changes per employee.

Class constant

<?php
class Config {
  public const SITE_NAME = "Rishtaara";
  public const MAX_UPLOAD_MB = 5;
}

echo Config::SITE_NAME;
echo Config::MAX_UPLOAD_MB . " MB max";
?>