Magic Methods
The behaviour of FINAL is not as serious as you may think. A little explample:
<?php
class A {
final private function method(){}
}
class B extends A {
private function method(){}
}
?>
Normally you would expect some of the following will happen:
- An error that final and private keyword cannot be used together
- No error as the private visibility says, that a method/var/etc. is only visible within the same class
But what happens is PHP is a little curios: "Cannot override final method A::method()"
So its possible to deny method names in subclasses! Don't know if this is a good behavior, but maybe its useful for your purpose.
Final Keyword
PHP 5 introduces the final keyword, which prevents child classes from overriding a method by prefixing the definition with final. If the class itself is being defined final then it cannot be extended.
Przykład #1 Final methods example
<?php
class BaseClass {
public function test() {
echo "BaseClass::test() called\n";
}
final public function moreTesting() {
echo "BaseClass::moreTesting() called\n";
}
}
class ChildClass extends BaseClass {
public function moreTesting() {
echo "ChildClass::moreTesting() called\n";
}
}
// Results in Fatal error: Cannot override final method BaseClass::moreTesting()
?>
Przykład #2 Final class example
<?php
final class BaseClass {
public function test() {
echo "BaseClass::test() called\n";
}
// Here it doesn't matter if you specify the function as final or not
final public function moreTesting() {
echo "BaseClass::moreTesting() called\n";
}
}
class ChildClass extends BaseClass {
}
// Results in Fatal error: Class ChildClass may not inherit from final class (BaseClass)
?>
Informacja: Properties cannot be declared final, only classes and methods may be declared as final.
add a note
User Contributed Notes
Final Keyword
Anonymous
28-Sep-2010 01:06
Baldurien
31-Aug-2010 07:37
"Note for Java developers: the 'final' keyword is not used for class constants in PHP. We use the keyword 'const'."
http://php.net/manual/en/language.oop5.constants.php
This is more or less true, regardless of the fact that constant (being defined at class level or not) in PHP are only scalar (int, string, etc) while in Java they may be pure object (ex: java.awat.Color.BLACK). The only possible solution of having such kind of constant is :
<?php
class Bar {...}
class Foo {
public static $FOOBAR;
static function __init() {
static $init = false;
if ($init) throw new Exception('Constants were already initialized');
self::$FOOBAR = new Bar();
$init = true;
}
}
Foo::__init();
?>
That said, perhaps it is useless unless PHP automatically calls the __init() method.
However, one alternative that could be done in certain case is this :
<?php
function __autoload($className) {
... require the file where the class is ...
if (interface_exists($className, false)) return;
if (class_exists($className, false)) {
$rc = new ReflectionClass($className);
if (!$rc->hasMethod('__init')) return;
$m = $rc->getMethod('__init');
if (!($m->isStatic() && $m->isPrivate())) {
throw new Exception($className . ' __init() method must be private and static !');
}
$m->invoke(null);
return;
}
throw new Exception('Class or interface not found ' . $className);
}
?>
This can only work when one class is defined per file, since we are assured that __autoload() will be called to load the file containing the class.
eg:
test2.php:
<?php
class B {
public static $X;
private static function __init() {
echo 'B', "\n";
self::$X = array(1, 2);
}
}
class A {
public static $Y;
private static function __init() {
echo 'A', "\n";
self::$Y = array(3, 4);
}
}
?>
test.php:
<?php
function __autoload($n) {
if ($n == 'A' || $n == 'B') require 'test2.php';
... do our __init() trick ...
}
var_dump(B::$X); // shows B, then array(2) (1, 2)
var_dump(A::$Y); // shows NULL.
?>
Kiam
31-Jul-2009 10:49
The final keyword doesn't change the visibility of a property / method, which is public by default.
jriddy at gmail dot com
17-Jul-2009 08:20
Note for Java developers: the 'final' keyword is not used for class constants in PHP. We use the keyword 'const'.
http://php.net/manual/en/language.oop5.constants.php
sunil dot boodram at gmail dot com
18-Mar-2009 03:54
Using the scope resolution operator, we can easily access constants, static variables, public functions and final functions from Final Classes
Note: even by omitting the "public" keyword from the "nightNews()" method, we can see that the function defaults to public even if prefixed with the keyword final.
<?php
final class news{
const micCheck = "test1"; // will work
static public $promptCheck = "test2"; //will work
//will work
public function morningNews(){
print 'good morning world!';
}
//will work
final public function eveningNews(){
print 'good evening world!';
}
//will work
final function nightNews(){
print 'good night world!';
}
}
print news::micCheck; // output: test1
print '<br/>';
print news::$promptCheck; // output: test2
print '<br/>';
print news::morningNews(); // output: good morning world!
print '<br/>';
print news::eveningNews(); // output: good evening world!
print '<br/>';
print news::nightNews(); // output: good night world!
?>
santoshjoshi2003 at yahoo dot co dot in
04-Dec-2008 07:45
The use of final keyword is just like that occurs in Java
In java final has three uses
1) prevent class Inheritance
2) prevent method overriding or redifination of
method in subclass
3) and to declare constants
But the third point seems to be missing from the PHP
I guess, as i am a java developer Currently gaining competence in PHP
slorenzo at clug dot org dot ve
30-Oct-2007 05:13
<?php
class parentClass {
public function someMethod() { }
}
class childClass extends parentClass {
public final function someMethod() { } //override parent function
}
$class = new childClass;
$class->someMethod(); //call the override function in chield class
?>
penartur at yandex dot ru
21-Mar-2007 07:39
Note that you cannot ovverride final methods even if they are defined as private in parent class.
Thus, the following example:
<?php
class parentClass {
final private function someMethod() { }
}
class childClass extends parentClass {
private function someMethod() { }
}
?>
dies with error "Fatal error: Cannot override final method parentClass::someMethod() in ***.php on line 7"
Such behaviour looks slight unexpected because in child class we cannot know, which private methods exists in a parent class and vice versa.
So, remember that if you defined a private final method, you cannot place method with the same name in child class.