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Visibility

The visibility of a property, a method or (as of PHP 7.1.0) a constant can be defined by prefixing the declaration with the keywords public, protected or private. Class members declared public can be accessed everywhere. Members declared protected can be accessed only within the class itself and by inheriting and parent classes. Members declared as private may only be accessed by the class that defines the member.

Property Visibility

Class properties must be defined as public, private, or protected. If declared using var, the property will be defined as public.

Example #1 Property 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 properties, but not private
    
public $public 'Public2';
    protected 
$protected 'Protected2';

    function 
printHello()
    {
        echo 
$this->public;
        echo 
$this->protected;
        echo 
$this->private;
    }
}

$obj2 = new MyClass2();
echo 
$obj2->public// Works
echo $obj2->protected// Fatal Error
echo $obj2->private// Undefined
$obj2->printHello(); // Shows Public2, 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 may be defined as public, private, or protected. Methods declared without any explicit visibility keyword 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
?>

Constant Visibility

As of PHP 7.1.0, class constants may be defined as public, private, or protected. Constants declared without any explicit visibility keyword are defined as public.

Example #3 Constant Declaration as of PHP 7.1.0

<?php
/**
 * Define MyClass
 */
class MyClass
{
    
// Declare a public constant
    
public const MY_PUBLIC 'public';

    
// Declare a protected constant
    
protected const MY_PROTECTED 'protected';

    
// Declare a private constant
    
private const MY_PRIVATE 'private';

    public function 
foo()
    {
        echo 
self::MY_PUBLIC;
        echo 
self::MY_PROTECTED;
        echo 
self::MY_PRIVATE;
    }
}

$myclass = new MyClass();
MyClass::MY_PUBLIC// Works
MyClass::MY_PROTECTED// Fatal Error
MyClass::MY_PRIVATE// Fatal Error
$myclass->foo(); // Public, Protected and Private work


/**
 * Define MyClass2
 */
class MyClass2 extends MyClass
{
    
// This is public
    
function foo2()
    {
        echo 
self::MY_PUBLIC;
        echo 
self::MY_PROTECTED;
        echo 
self::MY_PRIVATE// Fatal Error
    
}
}

$myclass2 = new MyClass2;
echo 
MyClass2::MY_PUBLIC// Works
$myclass2->foo2(); // Public and Protected work, not Private
?>

Visibility from other objects

Objects of the same type will have access to each others private and protected members even though they are not the same instances. This is because the implementation specific details are already known when inside those objects.

Example #4 Accessing private members of the same object type

<?php
class Test
{
    private 
$foo;

    public function 
__construct($foo)
    {
        
$this->foo $foo;
    }

    private function 
bar()
    {
        echo 
'Accessed the private method.';
    }

    public function 
baz(Test $other)
    {
        
// We can change the private property:
        
$other->foo 'hello';
        
var_dump($other->foo);

        
// We can also call the private method:
        
$other->bar();
    }
}

$test = new Test('test');

$test->baz(new Test('other'));
?>

The above example will output:

string(5) "hello"
Accessed the private method.
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