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Ключевое слово static

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Эта страница описывает использование ключевого слова static для определения статических методов и свойств. static также может использоваться для определения статических переменных и позднего статического связывания. Для получения информации о таком применении ключевого слова static обратитесь по вышеуказанным страницам.

Объявление свойств и методов класса статическими позволяет обращаться к ним без создания экземпляра класса. Свойство класса, объявленное как статическое, не может быть доступно посредством экземпляра класса (но статический метод может быть вызван).

В целях совместимости с PHP 4, если определение области видимости не используется, то свойство или метод будут обрабатываться так, как если бы он был объявлен как public.

Статические методы

Так как статические методы вызываются без создания экземпляра класса, то псевдопеременная $this недоступна внутри метода, объявленного как статический.

Предостережение

В PHP 5 вызов нестатических методов статически вызовет ошибку уровня E_STRICT.

Внимание

В PHP 7 вызов нестатических методов статически объявлен устаревшим и вызовет ошибку уровня E_DEPRECATED. Поддержка вызова нестатических методов статически может быть удалена в будущем.

Пример #1 Пример статического метода

<?php
class Foo {
    public static function 
aStaticMethod() {
        
// ...
    
}
}

Foo::aStaticMethod();
$classname 'Foo';
$classname::aStaticMethod(); // Начиная с PHP 5.3.0
?>

Статические свойства

Статические свойства не могут быть доступны через объект с помощью оператора "->".

Как и любая другая статическая переменная PHP, статические свойства могут инициализироваться только используя литерал или константу до PHP 5.6; выражения не допускается. В PHP 5.6 и более новых версиях применяются те же правила, что и для выражений const: возможны некоторые выражения, если они могут быть вычислены во время компиляциии.

Начиная с PHP 5.3.0, существует возможность ссылаться на класс используя переменную. Значение переменной в таком случае не может быть ключевым словом (например, self, parent и static).

Пример #2 Пример статического свойства

<?php
class Foo
{
    public static 
$my_static 'foo';

    public function 
staticValue() {
        return 
self::$my_static;
    }
}

class 
Bar extends Foo
{
    public function 
fooStatic() {
        return 
parent::$my_static;
    }
}


print 
Foo::$my_static "\n";

$foo = new Foo();
print 
$foo->staticValue() . "\n";
print 
$foo->my_static "\n";      // Не определено свойство my_static

print $foo::$my_static "\n"// Начиная с PHP 5.3.0
$classname 'Foo';
print 
$classname::$my_static "\n"// Начиная с PHP 5.3.0

print Bar::$my_static "\n";
$bar = new Bar();
print 
$bar->fooStatic() . "\n";
?>
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User Contributed Notes 26 notes

up
155
inkredibl
11 years ago
Note that you should read "Variables/Variable scope" if you are looking for static keyword use for declaring static variables inside functions (or methods). I myself had this gap in my PHP knowledge until recently and had to google to find this out. I think this page should have a "See also" link to static function variables.
http://www.php.net/manual/en/language.variables.scope.php
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115
payal001 at gmail dot com
8 years ago
Here statically accessed property prefer property of the class for which it is called. Where as self keyword enforces use of current class only. Refer the below example:

<?php
class a{

static protected
$test="class a";

public function
static_test(){

echo static::
$test; // Results class b
echo self::$test; // Results class a

}

}

class
b extends a{

static protected
$test="class b";

}

$obj = new b();
$obj->static_test();
?>
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12
artekpuck at gmail dot com
1 year ago
It is worth mentioning that there is only one value for each static variable that is the same for all instances
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6
ASchmidt at Anamera dot net
1 year ago
It is important to understand the behavior of static properties in the context of class inheritance:

- Static properties defined in both parent and child classes will hold DISTINCT values for each class. Proper use of self:: vs. static:: are crucial inside of child methods to reference the intended static property.

- Static properties defined ONLY in the parent class will share a COMMON value.

<?php
declare(strict_types=1);

class
staticparent {
    static   
$parent_only;
    static   
$both_distinct;
   
    function
__construct() {
        static::
$parent_only = 'fromparent';
        static::
$both_distinct = 'fromparent';
    }
}

class
staticchild extends staticparent {
    static   
$child_only;
    static   
$both_distinct;
   
    function
__construct() {
        static::
$parent_only = 'fromchild';
        static::
$both_distinct = 'fromchild';
        static::
$child_only = 'fromchild';
    }
}

$a = new staticparent;
$a = new staticchild;

echo
'Parent: parent_only=', staticparent::$parent_only, ', both_distinct=', staticparent::$both_distinct, "<br/>\r\n";
echo
'Child:  parent_only=', staticchild::$parent_only, ', both_distinct=', staticchild::$both_distinct, ', child_only=', staticchild::$child_only, "<br/>\r\n";
?>

will output:
Parent: parent_only=fromchild, both_distinct=fromparent
Child: parent_only=fromchild, both_distinct=fromchild, child_only=fromchild
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13
webmaster at removethis dot weird-webdesign dot de
9 years ago
On PHP 5.2.x or previous you might run into problems initializing static variables in subclasses due to the lack of late static binding:

<?php
class A {
    protected static
$a;
   
    public static function
init($value) { self::$a = $value; }
    public static function
getA() { return self::$a; }
}

class
B extends A {
    protected static
$a; // redefine $a for own use
   
    // inherit the init() method
   
public static function getA() { return self::$a; }
}

B::init('lala');
echo
'A::$a = '.A::getA().'; B::$a = '.B::getA();
?>

This will output:
A::$a = lala; B::$a =

If the init() method looks the same for (almost) all subclasses there should be no need to implement init() in every subclass and by that producing redundant code.

Solution 1:
Turn everything into non-static. BUT: This would produce redundant data on every object of the class.

Solution 2:
Turn static $a on class A into an array, use classnames of subclasses as indeces. By doing so you also don't have to redefine $a for the subclasses and the superclass' $a can be private.

Short example on a DataRecord class without error checking:

<?php
abstract class DataRecord {
    private static
$db; // MySQLi-Connection, same for all subclasses
   
private static $table = array(); // Array of tables for subclasses
   
   
public static function init($classname, $table, $db = false) {
        if (!(
$db === false)) self::$db = $db;
       
self::$table[$classname] = $table;
    }
   
    public static function
getDB() { return self::$db; }
    public static function
getTable($classname) { return self::$table[$classname]; }
}

class
UserDataRecord extends DataRecord {
    public static function
fetchFromDB() {
       
$result = parent::getDB()->query('select * from '.parent::getTable('UserDataRecord').';');
       
       
// and so on ...
       
return $result; // An array of UserDataRecord objects
   
}
}

$db = new MySQLi(...);
UserDataRecord::init('UserDataRecord', 'users', $db);
$users = UserDataRecord::fetchFromDB();
?>

I hope this helps some people who need to operate on PHP 5.2.x servers for some reason. Late static binding, of course, makes this workaround obsolete.
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10
davidn at xnet dot co dot nz
10 years ago
Static variables are shared between sub classes

<?php
class MyParent {
   
    protected static
$variable;
}

class
Child1 extends MyParent {
   
    function
set() {
       
       
self::$variable = 2;
    }
}

class
Child2 extends MyParent {
   
    function
show() {
       
        echo(
self::$variable);
    }
}

$c1 = new Child1();
$c1->set();
$c2 = new Child2();
$c2->show(); // prints 2
?>
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4
Anonymous
6 years ago
It should be noted that in 'Example #2', you can also call a variably defined static method as follows:

<?php
class Foo {
    public static function
aStaticMethod() {
       
// ...
   
}
}

$classname = 'Foo';
$methodname = 'aStaticMethod';
$classname::{$methodname}(); // As of PHP 5.3.0 I believe
?>
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3
vinayak dot anivase at gmail dot com
1 year ago
This is also possible:

class Foo {
  public static $bar = 'a static property';
}

$baz = (new Foo)::$bar;
echo $baz;
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10
aidan at php dot net
14 years ago
To check if a function was called statically or not, you'll need to do:

<?php
function foo () {
   
$isStatic = !(isset($this) && get_class($this) == __CLASS__);
}
?>

More at (http://blog.phpdoc.info/archives/4-Schizophrenic-Methods.html).

(I'll add this to the manual soon).
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5
tolean_dj at yahoo dot com
8 years ago
Starting with php 5.3 you can get use of new features of static keyword. Here's an example of abstract singleton class:

<?php

abstract class Singleton {

    protected static
$_instance = NULL;

   
/**
     * Prevent direct object creation
     */
   
final private function  __construct() { }

   
/**
     * Prevent object cloning
     */
   
final private function  __clone() { }

   
/**
     * Returns new or existing Singleton instance
     * @return Singleton
     */
   
final public static function getInstance(){
        if(
null !== static::$_instance){
            return static::
$_instance;
        }
        static::
$_instance = new static();
        return static::
$_instance;
    }
   
}
?>
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5
ssj dot narutovash at gmail dot com
11 years ago
It's come to my attention that you cannot use a static member in an HEREDOC string.  The following code

class A
{
  public static $BLAH = "user";

  function __construct()
  {
    echo <<<EOD
<h1>Hello {self::$BLAH}</h1>
EOD;
  }
}

$blah = new A();

produces this in the source code:

<h1>Hello {self::}</h1>

Solution:

before using a static member, store it in a local variable, like so:

class B
{
  public static $BLAH = "user";

  function __construct()
  {
    $blah = self::$BLAH;
    echo <<<EOD
<h1>Hello {$blah}</h1>
EOD;
  }
}

and the output's source code will be:

<h1>Hello user</h1>
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1
Anonymous
14 years ago
You misunderstand the meaning of inheritance : there is no duplication of members when you inherit from a base class. Members are shared through inheritance, and can be accessed by derived classes according to visibility (public, protected, private).

The difference between static and non static members is only that a non static member is tied to an instance of a class although a static member is tied to the class, and not to a particular instance.
That is, a static member is shared by all instances of a class although a non static member exists for each instance of  class.

Thus, in your example, the static property has the correct value, according to principles of object oriented conception.
class Base
{
  public $a;
  public static $b;
}

class Derived extends Base
{
  public function __construct()
  {
    $this->a = 0;
    parent::$b = 0;
  }
  public function f()
  {
    $this->a++;
    parent::$b++;
  }
}

$i1 = new Derived;
$i2 = new Derived;

$i1->f();
echo $i1->a, ' ', Derived::$b, "\n";
$i2->f();
echo $i2->a, ' ', Derived::$b, "\n";

outputs
1 1
1 2
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2
Jay Cain
9 years ago
Regarding the initialization of complex static variables in a class, you can emulate a static constructor by creating a static function named something like init() and calling it immediately after the class definition.

<?php
class Example {
    private static
$a = "Hello";
    private static
$b;

    public static function
init() {
       
self::$b = self::$a . " World!";
    }
}
Example::init();
?>
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4
gratcypalma at gmail dot om
8 years ago
<?php
class foo {
    private static
$getInitial;

    public static function
getInitial() {
        if (
self::$getInitial == null)
           
self::$getInitial = new foo();
        return
self::$getInitial;
    }
}

foo::getInitial();

/*
this is the example to use new class with static method..
i hope it help
*/

?>
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3
michalf at ncac dot torun dot pl
14 years ago
Inheritance with the static elements is a nightmare in php. Consider the following code:

<?php
class BaseClass{
    public static
$property;
}

class
DerivedClassOne extends BaseClass{
}

class
DerivedClassTwo extends BaseClass{
}

DerivedClassOne::$property = "foo";
DerivedClassTwo::$property = "bar";

echo
DerivedClassOne::$property; //one would naively expect "foo"...
?>

What would you expect as an output? "foo"? wrong. It is "bar"!!! Static variables are not inherited, they point to the BaseClass::$property.

At this point I think it is a big pity inheritance does not work in case of static variables/methods. Keep this in mind and save your time when debugging.

best regards - michal
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2
Mirco
9 years ago
The simplest static constructor.

Because php does not have a static constructor and you may want to initialize static class vars, there is one easy way, just call your own function directly after the class definition.

for example.

<?php
function Demonstration()
{
    return
'This is the result of demonstration()';
}

class
MyStaticClass
{
   
//public static $MyStaticVar = Demonstration(); //!!! FAILS: syntax error
   
public static $MyStaticVar = null;

    public static function
MyStaticInit()
    {
       
//this is the static constructor
        //because in a function, everything is allowed, including initializing using other functions
       
       
self::$MyStaticVar = Demonstration();
    }
}
MyStaticClass::MyStaticInit(); //Call the static constructor

echo MyStaticClass::$MyStaticVar;
//This is the result of demonstration()
?>
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1
vvikramraj at yahoo dot com
11 years ago
when attempting to implement a singleton class, one might also want to either
a) disable __clone by making it private
b) bash the user who attempts to clone by defining __clone to throw an exception
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1
zerocool at gameinsde dot ru
11 years ago
Hi, here's my simple Singleton example, i think it can be useful for someone. You can use this pattern to connect to the database for example.

<?php

 
class MySingleton
 
{
    private static
$instance = null;

    private function
__construct()
    {
     
$this-> name = 'Freddy';

    }

    public static function
getInstance()
    {
      if(
self::$instance == null)
      {
        print
"Object created!<br>";
       
self::$instance = new self;

      }

      return
self::$instance;

    }

    public function
sayHello()
    {
      print
"Hello my name is {$this-> name}!<br>";

    }

    public function
setName($name)
    {
     
$this-> name = $name;

    }

  }

 
//

 
$objA = MySingleton::getInstance(); // Object created!

 
$objA-> sayHello(); // Hello my name is Freddy!

 
$objA-> setName("Alex");

 
$objA-> sayHello(); // Hello my name is Alex!

 
$objB = MySingleton::getInstance();

 
$objB-> sayHello(); // Hello my name is Alex!

 
$objB-> setName("Bob");

 
$objA-> sayHello(); // Hello my name is Bob!

?>
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0
b1tchcakes
3 years ago
<?php

trait t {
  protected
$p;
  public function
testMe() {echo 'static:'.static::class. ' // self:'.self::class ."\n";}
}

class
a { use t; }
class
b extends a {}

echo (new
a)->testMe();
echo (new
b)->testMe();

outputs
static:a // self:t
static:b // self:t
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0
rahul dot anand77 at gmail dot com
4 years ago
To check if a method declared in a class is static or not, you can us following code. PHP5 has a Reflection Class, which is very helpful.

try {
    $method = new ReflectionMethod( 'className::methodName );
    if ( $method->isStatic() )
    {
        // Method is static.
    }
}
catch ( ReflectionException $e )
{
    //    method does not exist
    echo $e->getMessage();
}

*You can read more about Reflection class on http://php.net/manual/en/class.reflectionclass.php
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0
sideshowAnthony at googlemail dot com
4 years ago
The static keyword can still be used (in a non-oop way) inside a function. So if you need a value stored with your class, but it is very function specific, you can use this:

class aclass {
    public static function b(){
        static $d=12; // Set to 12 on first function call only
        $d+=12;
        return "$d\n";
    }
}

echo aclass::b(); //24
echo aclass::b(); //36
echo aclass::b(); //48
echo aclass::$d; //fatal error
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0
jkenigso at utk dot edu
5 years ago
It bears mention that static variables (in the following sense) persist:

<?php
class StaticVars
{
  public static
$a=1;
}
$b=new StaticVars;
$c=new StaticVars;

echo
$b::$a; //outputs 1
$c::$a=2;
echo
$b::$a; //outputs 2!
?>

Note that $c::$a=2 changed the value of $b::$a even though $b and $c are totally different objects.
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0
manishpatel2280 at gmail dot com
5 years ago
In real world, we can say will use static method when we dont want to create object instance.

e.g ...

validateEmail($email) {
if(T) return true;
return false;
}

//This makes not much sense
$obj = new Validate();
$result = $obj->validateEmail($email);

//This makes more sense
$result = Validate::validateEmail($email);
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-1
valentin at balt dot name
9 years ago
How to implement a one storage place based on static properties.

<?php
class a {
   
    public function
get () {
        echo
$this->connect();
    }
}
class
b extends a {
    private static
$a;

    public function
connect() {
        return
self::$a = 'b';
    }
}
class
c extends a {
    private static
$a;

    public function
connect() {
        return
self::$a = 'c';
    }
}
$b = new b ();
$c = new c ();

$b->get();
$c->get();
?>
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-1
Mathijs Vos
11 years ago
<?php
class foo
{
    public static
$myStaticClass;
   
    public function
__construct()
    {
       
self::myStaticClass = new bar();
    }
}

class
bar
{
        public function
__construct(){}
}
?>

Please note, this won't work.
Use self::$myStaticClass = new bar(); instead of self::myStaticClass = new bar(); (note the $ sign).
Took me an hour to figure this out.
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-2
michael at digitalgnosis dot removethis dot com
14 years ago
If you are trying to write classes that do this:

<?php

class Base
{
    static function
Foo ()
    {
       
self::Bar();
    }
}

class
Derived extends Base
{
    function
Bar ()
    {
        echo
"Derived::Bar()";
    }
}

Derived::Foo(); // we want this to print "Derived::Bar()"

?>

Then you'll find that PHP can't (unless somebody knows the Right Way?) since 'self::' refers to the class which owns the /code/, not the actual class which is called at runtime. (__CLASS__ doesn't work either, because: A. it cannot appear before ::, and B. it behaves like 'self')

But if you must, then here's a (only slightly nasty) workaround:

<?php

class Base
{
    function
Foo ( $class = __CLASS__ )
    {
       
call_user_func(array($class,'Bar'));
    }
}

class
Derived extends Base
{
    function
Foo ( $class = __CLASS__ )
    {
       
parent::Foo($class);
    }

    function
Bar ()
    {
        echo
"Derived::Bar()";
    }
}

Derived::Foo(); // This time it works. 

?>

Note that Base::Foo() may no longer be declared 'static' since static methods cannot be overridden (this means it will trigger errors if error level includes E_STRICT.)

If Foo() takes parameters then list them before $class=__CLASS__ and in most cases, you can just forget about that parameter throughout your code.

The major caveat is, of course, that you must override Foo() in every subclass and must always include the $class parameter when calling parent::Foo().
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