PHP: Visibility

Visibility

The visibility of a property or method can be defined by prefixing the declaration with the keywords: public, protected or private. Public declared items can be accessed everywhere. Protected limits access to inherited and parent classes (and to the class that defines the item). Private limits visibility only to the class that defines the item.

Members Visibility

Class members must be defined with public, private, or protected.

Example #1 Member declaration


<?php

/**

 * Define MyClass

 */

class MyClass

{

    public $public = 'Public';

    protected $protected = 'Protected';

    private $private = 'Private';



    function printHello()

    {

        echo $this->public;

        echo $this->protected;

        echo $this->private;

    }

}



$obj = new MyClass();

echo $obj->public; // Works

echo $obj->protected; // Fatal Error

echo $obj->private; // Fatal Error

$obj->printHello(); // Shows Public, Protected and Private





/**

 * Define MyClass2

 */

class MyClass2 extends MyClass

{

    // We can redeclare the public and protected method, but not private

    protected $protected = 'Protected2';



    function printHello()

    {

        echo $this->public;

        echo $this->protected;

        echo $this->private;

    }

}



$obj2 = new MyClass2();

echo $obj2->public; // Works

echo $obj2->private; // Undefined

echo $obj2->protected; // Fatal Error

$obj2->printHello(); // Shows Public, Protected2, Undefined



?>

Note: The PHP 4 method of declaring a variable with the var keyword is still supported for compatibility reasons (as a synonym for the public keyword). In PHP 5 before 5.1.3, its usage would generate an E_STRICT warning.

Method Visibility

Class methods must be defined with public, private, or protected. Methods without any declaration are defined as public.

Example #2 Method Declaration


<?php

/**

 * Define MyClass

 */

class MyClass

{

    // Declare a public constructor

    public function __construct() { }



    // Declare a public method

    public function MyPublic() { }



    // Declare a protected method

    protected function MyProtected() { }



    // Declare a private method

    private function MyPrivate() { }



    // This is public

    function Foo()

    {

        $this->MyPublic();

        $this->MyProtected();

        $this->MyPrivate();

    }

}



$myclass = new MyClass;

$myclass->MyPublic(); // Works

$myclass->MyProtected(); // Fatal Error

$myclass->MyPrivate(); // Fatal Error

$myclass->Foo(); // Public, Protected and Private work





/**

 * Define MyClass2

 */

class MyClass2 extends MyClass

{

    // This is public

    function Foo2()

    {

        $this->MyPublic();

        $this->MyProtected();

        $this->MyPrivate(); // Fatal Error

    }

}



$myclass2 = new MyClass2;

$myclass2->MyPublic(); // Works

$myclass2->Foo2(); // Public and Protected work, not Private



class Bar 

{

    public function test() {

        $this->testPrivate();

        $this->testPublic();

    }



    public function testPublic() {

        echo "Bar::testPublic\n";

    }

    

    private function testPrivate() {

        echo "Bar::testPrivate\n";

    }

}



class Foo extends Bar 

{

    public function testPublic() {

        echo "Foo::testPublic\n";

    }

    

    private function testPrivate() {

        echo "Foo::testPrivate\n";

    }

}



$myFoo = new foo();

$myFoo->test(); // Bar::testPrivate 

                // Foo::testPublic

?>