PHP Visibility modes

Introduction

In PHP, it is possible to have a user-defined compund data type using class keyword. A new instance of class is an object. Charactersitics of object are as per definition of class, which may contain property, constant and method members.

Accessibility (also called visibility) of a class member depends on visibility prefix keyword attached in its definition. PHP has three visibility keywords - public, private and protected. A class member declared with public keyword is accessible from anywhare. A protected member is accessible from within its class and by inheriting class. On the other hand, a private member can only be accessed by the same class in which it is defined and is not visible to anything outside it.

Property Visibility

A property is an attribute of class instance. It may be an instance property (having different value for each object) or class property with same value for each object. A property may be of any valid PHP data type. A property has public visibility by default. If a property is defined using var keyword (which has been deprecated now), it is treated as public.

Example

 Live Demo

<?php
class myclass{
   public $fname="Ajay";
   var $lname; //treated as public
   private $marks=100;
   protected $age=20;
}
$obj=new myclass();
echo "$obj->fname
";
$obj->lname="Diwan";
echo "$obj->marks
";
$obj->age=21;
?>

Output

Following output shows that public properties can be accessed outside class, while private and protected propeties throw uncaught errors

Ajay
PHP Fatal error: Uncaught Error: Cannot access private property myclass::$marks
PHP Fatal error: Uncaught Error: Cannot access protected property myclass::$age

However, private and protected properties can be used inside function in the same class

Example

 Live Demo

<?php
class myclass{
   public $fname="Ajay";
   var $lname;
   private $marks=100;
   protected $age=20;
   function displaydata(){
      $this->lname="Diwan";
      echo "$this->fname $this->lname
";
      echo "marks=$this->marks age=$this->age";
   }
}
$obj=new myclass();
$obj->displaydata();
?>

Output

This will produce following result. −

Ajay Diwan
marks=100 age=20

Method Visibility

Like class properties, class methods can also be assigned visibility with public, private and protected keywords. Methods too, by default are treated as public.

Example

<?php
class myclass{
   public $fname="Ajay";
   var $lname;
   private $marks=100;
   protected $age=20;
   public function setname(){
      $this->fname="Anil";
      $this->lname="Dave";
      echo "name changed
";
   }
   private function setmarks(){
      $this->marks=90;
   }
   protected function setage(){
      $this->age=21;
   }
   function setdata(){
      $this->setname();
      $this->setmarks();
      $this->setage();
   }
   function displaydata(){
      $this->lname="Diwan";
      echo "$this->fname $this->lname
";
      echo "marks=$this->marks age=$this->age";
   }
}
$obj=new myclass();
$obj->setname();//works
$obj->setmarks();//error
$obj->setage();/error
$obj->setdata(); //private and protected methods called withing public method
$obj->displaydata();
?>

Output

This will produce following result. −

name changed
PHP Fatal error: Uncaught Error: Call to private method myclass::setmarks() from context ''
PHP Fatal error: Uncaught Error: Call to protected method myclass::setage() from context ''
Anil Dave
marks=90 age=21

Method Visibility in Inheritance

Parent class methods can be overridden in child class definition. Private and protected methods of parent are not available for object of child class. A method that is protected in parent can however be used in a child class method

Example

 Live Demo

<?php
class testclass{
   public $x=10;
   private $y=20;
   protected $z=30;
   private function test(){
      echo "testclass private method
";
   }
   public function test1(){
      echo "testclass public method
";
   }
   protected function test2(){
      echo "testclass protected method
";
   }
   function test3(){
      echo "x=$this->x y=$this->y z=$this->z
";
   }
}
class newclass extends testclass{
   function test1(){
      echo "newclass public method
";
   }
   public function test4(){
      $this->test();
      $this->test1();
      $this->test2();
   }
}
$obj=new newclass();
echo $obj->test1();
echo $obj->test3();
echo $obj->test4();
?>

Output

This will show following result

newclass public method
x=10 y=20 z=30
PHP Fatal error: Uncaught Error: Call to private method testclass::test() from context 'newclass'

Constant Visibility

From PHP 7.1 onwards, visibility modes can be used with constaants. Default visibility of constant is public

Example

 Live Demo

<?php
class testclass{
   public const X=10;
   private const Y=20;
   protected const Z=30;
   function showconst(){
      echo "x=" . self::X ;
      echo "y=" . self::Y;
      echo "z=" . self::Z ;
   }
}
$obj=new testclass();
$obj->showconst();
echo testclass::Y . "
";
echo testclass::Z . "
";
?>

Output

This will show following result

x=10y=20z=30
PHP Fatal error: Uncaught Error: Cannot access private const testclass::Y
PHP Fatal error: Uncaught Error: Cannot access protected const testclass::Z