OOP Basics: Access Modifiers

Access modifiers determine the visibility of properties and methods within your classes. With them, we precisely control which parts of the code can see, read, or modify the data inside an object. This is a fundamental concept of object-oriented programming called encapsulation (data hiding), which prevents external code from accidentally or unauthorizedly altering critical system data.

EXAMPLE

<?php
class Vehicle {
    public $brand; // Accessible to everyone
    protected $model; // Accessible to the class and children (inheritors)
    private $serialNumber; // Accessible only within this class

public function __construct($brand, $model, $sn) {
        $this->brand = $brand;
        $this->model = $model;
        $this->serialNumber = $sn;
    }

public function getSerialNumber() {
        return $this->serialNumber; // Own method sees private data
    }
}

class Car extends Vehicle {
    public function displayModel() {
        // Using a dot for string concatenation prevents errors in the simulator
        return "Vehicle model: " . $this->model;
    }
}

$myCar = new Car("Tesla", "Model S", "XYZ123");

echo $myCar->brand . "<br>"; // WORKS: Tesla
echo $myCar->displayModel() . "<br>"; // WORKS: Model S
// echo $myCar->model; // ERROR: Protected is not accessible outside
// echo $myCar->serialNumber; // ERROR: Private is not accessible outside
echo $myCar->getSerialNumber(); // WORKS: XYZ123 (via public method)
?>

RESULT

The result will be displayed here...

Visibility Levels in PHP

PHP offers three main access modifiers, which we write right before the definition of a variable or method:

Modifier	Visibility and Accessibility
`public`	Accessible to everyone: Properties and methods are visible from anywhere – inside the class, in subclasses, and in external code.
`protected`	Accessible to the family (Inheritance): Visible only within the same class and in all subclasses that inherit from it (extends). External code has no access.
`private`	Strictly private: Visible exclusively within the class where it is defined. Subclasses (children) cannot see or modify this data.

Real-World Analogy: Your Own House

If we map the levels of visibility to everyday life, you can imagine them as spaces in your house:

Public (Living Room/Yard): A space where any passerby or guest (external code) can enter. There are things there that you have no trouble showing to everyone.
Protected (Family Garage): A space that only members of your immediate family (subclasses) can access. Neighbors from the street cannot get into it, but your children can use it freely.
Private (Private Safe): A safe in the bedroom is accessible solely and exclusively to you personally (the original class). Not even your own children have a key to peek inside.