Access Modifiers in PHP

In PHP, access modifiers are an important part of object-oriented programming (OOP). They specify the scope of class variables or methods and how they can be accessed. In this post, we will look at the different types of access modifiers in PHP and offer examples of how to use them.

Access Modifier Types in PHP

In PHP, access modifiers are classified as public, private, or protected.

Public: A method or attribute that is set to public can be accessed everywhere. This is the default access modifier in PHP.
Private: A method or attribute that is set to private can only be accessed within the class in which it is created.
Protected: A method or attribute that is set to protected can be accessed within the class in which it is created, as well as in classes that inherit from that class.

Examples

class Person{
  public $name;
  protected $age;
  private $height;
}

$x= new Person();
$x->name = 'John'; // OK
$x->age= '32'; // ERROR
$x->height= '5.4'; // ERROR

In the above example, we define a “Person” class with three attributes, each with a separate access modifier. The “name” attribute is public, the “age” attribute is protected, and the “height” attribute is private. When we try to access the “name” attribute outside of the class and add a value to it, everything works fine. However, attempting to add values to the “age” and “height” properties outside of the class results in a fatal error.

Public, Private, and Protected Methods

class Person{
  public $name;
  public $age;
  public $height;

  function set_name($n) {  // a public function (default)
    $this->name = $n;
  }
  protected function set_age($a) { // a protected function
    $this->age = $a;
  }
  private function set_height($h) { // a private function
    $this->height = $h;
  }
}

$person = new Person();
$person->set_name('John'); // OK
$person->set_age('26'); // ERROR
$person->set_height('5.4'); // ERROR

In the above example, we build a “Person” class with three methods, each with a separate access modifier. The “set name” method is public, the “set age” method is protected, and the “set height” method is private. When we try to invoke the “set name” function from outside the class, it works well. When we try to call the “set age” and “set height” methods from outside the class, we get a fatal error.

Advanced Access Modifiers: Abstract and Final

PHP provides sophisticated access modifiers named “abstract” and “final” in addition to the regular access modifiers.

An abstract access modifier can only be used on classes and methods. It is used to construct a class blueprint, however the class cannot be instantiated. Abstract methods are methods that every class that inherits from the abstract class must implement.
Classes, methods, and properties can all be given a final access modifier. It is used to prohibit a class or method from being extended or overridden.

Examples

abstract class Bike {

    private $maxSpeed = 80;

    // Simple method
    public function drivingSpeed() {
        return "Driving at " . $this->maxSpeed . " kilometer/hour";
    }

    // Abstract method
    abstract public function drive();
}

class Police extends Bike {

    public function drive() {
        return "Driving out of speed limit.";
    }

}

$bike= new Police();
echo $bike->drivingSpeed();

In the example above, we build an abstract class named “Bike” that has an abstract function called “drive()”. We next construct a new class named “Police,” which extends the “Bike” class and implements the “drive()” function. We use the “Police” class instead because we can’t build an object of the abstract class.

Finally, access modifiers are an important part of OOP in PHP and are used to limit the scope of class variables or functions. Understanding and effectively using access modifiers may help you develop more secure and maintainable code.

Q&A

Q: What are access modifiers?
A: Access modifiers define the scope of class variables or methods, as well as where they may be accessed. In PHP, access modifiers are classified as public, private, or protected.

Q: What is the default access modifier?
A: PHP’s default access modifier is public. If you do not provide the access modifier while creating a method or attribute in a PHP class, it is set to public by default.

Q: What is the difference between private and protected access modifiers?
A: A private method or attribute may only be accessible within the class that generated it, but a protected method or attribute can be accessed within the class that created it as well as classes that inherited from that class.

Q: Can you give an example of using an abstract access modifier in PHP?

abstract class Bike {
    private $maxSpeed = 80;
    abstract public function drive();
}
class Police extends Bike {
    public function drive() {
        return "Driving out of speed limit.";
    }
}

Q: How does the final access modifier work?
A: The final access modifier can be applied to classes, methods, and properties. It is used to prevent a class from being extended or a method from being overridden. This means that any class that inherits from a final class cannot be extended, and any method that is marked as final cannot be overridden.

Exercises:

What is the default access modifier in PHP?
What is the difference between private and protected access modifiers in PHP?
Give an example of using an abstract access modifier in PHP.
How does the final access modifier work?
Can you create an object of an abstract class? Why or why not?
Can you override a final method in a child class? Why or why not?
Can you assign a value to a private attribute outside of the class in which it is created? Why or why not?
Can a protected method be accessed outside of the class in which it is created? Why or why not?

Answers:

The default access modifier in PHP is public.
A private method or attribute in PHP can only be accessed within the class in which it is created, whereas a protected method or attribute can be accessed within the class in which it is created, as well as in classes that inherit from that class.

abstract class Bike {
    private $maxSpeed = 80;
    abstract public function drive();
}
class Police extends Bike {
    public function drive() {
        return "Driving out of speed limit.";
    }
}

4. The final access modifier can be applied to classes, methods, and properties. It is used to prevent a class from being extended or a method from being overridden.
5. No, we cannot create an object of an abstract class because an abstract class serves as a blueprint for other classes and does not have a constructor to create an object.
6. No, we cannot override a final method in a child class as it is marked as final and cannot be overridden.
7. No, we cannot provide a value to a private attribute outside of the class that generated it since the attribute is only available within the class.
8. No, a protected method cannot be accessible outside of the class that created it, but it may be accessed by classes that derive from that class.

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