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 may be defined as public, private, or protected. Properties declared without any explicit visibility keyword are defined as public.

Example #1 Property declaration

<?php

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



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

?>

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

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



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

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

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



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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