What is the difference between `public`, `protected`, and `private` visibility in PHP classes?

Introduction

In PHP, object-oriented programming (OOP) allows you to define the visibility of class properties and methods using three different access modifiers: `public`, `protected`, and `private`. Understanding these visibility levels is crucial for encapsulating data and controlling access to class members.

`public` Visibility

The `public` visibility modifier allows the class properties and methods to be accessible from anywhere, both inside and outside the class. This means that any code that has access to the class can interact with its public members.

Characteristics of `public`

• Accessibility: Accessible from any part of the code that has access to the class instance.
• Usage: Ideal for properties and methods that need to be accessible globally or by other objects.
• Example:

class MyClass {
public $property = "I am public";
public function display() {
echo $this->property;
}
}
$obj = new MyClass();
$obj->display(); // Output: I am public

`protected` Visibility

The `protected` visibility modifier restricts access to class properties and methods to the class itself and its subclasses. This means that protected members cannot be accessed from outside the class but can be accessed by classes that inherit from it.

Characteristics of `protected`

• Accessibility: Accessible within the class itself and by classes derived from it (subclasses).
• Usage: Useful for properties and methods that should be hidden from outside access but still available to subclasses.
• Example:

class ParentClass {
protected $property = "I am protected";
protected function display() {
echo $this->property;
}
}
class ChildClass extends ParentClass {
public function show() {
$this->display();
}
}
$obj = new ChildClass();
$obj->show(); // Output: I am protected

`private` Visibility

The `private` visibility modifier restricts access to class properties and methods to the class itself only. Private members cannot be accessed by subclasses or any external code. This ensures the highest level of encapsulation and data protection.

Characteristics of `private`

• Accessibility: Accessible only within the class itself.
• Usage: Best for sensitive data or methods that should not be exposed or modified from outside the class.
• Example:

class MyClass {
private $property = "I am private";
private function display() {
echo $this->property;
}
public function show() {
$this->display();
}
}
$obj = new MyClass();
$obj->show(); // Output: I am private
$obj->display(); // Error: Cannot access private method MyClass::display()

Key Differences Between `public`, `protected`, and `private`

1. Visibility: `public` is accessible from anywhere, `protected` is accessible within the class and its subclasses, and `private` is accessible only within the class itself.

2. Use Cases: Use `public` for globally accessible members, `protected` for inheritance-related access, and `private` for strict encapsulation.

3. Inheritance: `public` and `protected` members can be inherited, while `private` members cannot be accessed by subclasses.

Conclusion

Understanding the differences between `public`, `protected`, and `private` visibility levels in PHP is essential for designing secure and maintainable classes. By appropriately using these visibility modifiers, you can control access to your class members and enforce encapsulation.