PHP Access Modifiers

An access modifier (also called a visibility keyword) decides where a property or method can be used from.

PHP offers three of them:

public - available from anywhere; this is the default
protected - available inside the class and inside classes derived from it
private - available ONLY inside the class that defines it

Note: Leave the modifier out and PHP treats the property or method as public.

Public Access Modifier

Marking a property or method public means any code can reach it, inside or outside the class.

In the next example, code outside the class can use both the $name property and the get_details() method.

Public Example

Code outside the class sets a public property and calls a public method:

Write a PHP script that defines a Fruit class with a public $name property and a public get_details() method. Create a Fruit object, set its name directly, and display it.

> Output: PHP script

Prompt

Write a PHP script that defines a Fruit class with a public $name property and a public get_details() method. Create a Fruit object, set its name directly, and display it.

Output: PHP script

<?php
class Fruit {
  public $name;

  public function get_details() {
    echo "Name: " . $this->name . ".";
  }
}

$apple = new Fruit();
$apple->name = "Apple"; // Can be accessed directly
$apple->get_details();
?>

Private Access Modifier

private is the strictest modifier: only code inside the defining class can touch the property or method.

In the next example, $name is private, so reaching for it directly from outside the class fails.

Private Example

Assigning a value to a private property from outside the class causes a fatal error:

Write a PHP script that defines a Fruit class with a private $name property. Create a Fruit object and try to set the name property directly to show that it causes an error.

> Output: PHP script

Prompt

Write a PHP script that defines a Fruit class with a private $name property. Create a Fruit object and try to set the name property directly to show that it causes an error.

Output: PHP script

<?php
class Fruit {
  private $name;

  public function get_details() {
    echo "Name: " . $this->name . ".";
  }
}

$apple = new Fruit();
$apple->name = "Apple"; // Error: Cannot access private property
$apple->get_details();
?>

Protected Access Modifier

protected sits in between: the class itself and its derived classes (child classes) have access, but outside code does not.

In the next example, $name is protected, so direct access from outside is not allowed.

Protected Example

Assigning a value to a protected property from outside the class causes a fatal error:

Write a PHP script that defines a Fruit class with a protected $name property. Create a Fruit object and try to set the name directly to show that it causes an error.

> Output: PHP script

Prompt

Write a PHP script that defines a Fruit class with a protected $name property. Create a Fruit object and try to set the name directly to show that it causes an error.

Output: PHP script

<?php
class Fruit {
  protected $name;

  public function get_details() {
    echo "Name: " . $this->name . ".";
  }
}

$apple = new Fruit();
$apple->name = "Apple"; // Error: Cannot access protected property
$apple->get_details();
?>

Protected with Inheritance

A child class is allowed to read a protected property it inherited:

Write a PHP script that defines a Fruit class with a protected $name property and a setType() method. Then define an Apple class that extends Fruit and has a getType() method. Show that the protected property is accessible in the child class.

> Output: PHP script

Prompt

Write a PHP script that defines a Fruit class with a protected $name property and a setType() method. Then define an Apple class that extends Fruit and has a getType() method. Show that the protected property is accessible in the child class.

Output: PHP script

<?php
class Fruit {
  protected $name;

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

class Apple extends Fruit {
  public function getType() {
    echo "Name: " . $this->name . ".";
  }
}

$apple = new Apple();
$apple->setType("Apple");
echo $apple->getType();
?>