Php/docs/language.oop5.static
Static Keyword
Tip
This page describes the use of the static keyword to
define static methods and properties. static can also
be used to
define static variables
and for
late static bindings.
Please refer to those pages for information on those meanings of
static.
Declaring class properties or methods as static makes them accessible without needing an instantiation of the class. A property declared as static cannot be accessed with an instantiated class object (though a static method can).
For compatibility with PHP 4, if no visibility
declaration is used, then the property or method will be treated
as if it was declared as public.
Static methods
Because static methods are callable without an instance of
the object created, the pseudo-variable $this is
not available inside the method declared as static.
Caution
In PHP 5, calling non-static methods statically generates an
E_STRICT level warning.
Warning
In PHP 7, calling non-static methods statically is deprecated, and will
generate an E_DEPRECATED warning. Support for
calling non-static methods statically may be removed in the future.
Example #1 Static method example
<?phpclass Foo { public static function aStaticMethod() { // ... }}Foo::aStaticMethod();$classname = 'Foo';$classname::aStaticMethod(); // As of PHP 5.3.0?>
Static properties
Static properties cannot be accessed through the object using the arrow operator ->.
Like any other PHP static variable, static properties may only be
initialized using a literal or constant before PHP 5.6; expressions are
not allowed. In PHP 5.6 and later, the same rules apply as const
expressions: some limited expressions are possible, provided they can be
evaluated at compile time.
As of PHP 5.3.0, it's possible to reference the class using a variable.
The variable's value cannot be a keyword (e.g. self,
parent and static).
Example #2 Static property example
<?phpclass 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"; // Undefined "Property" my_static print $foo::$my_static . "\n";$classname = 'Foo';print $classname::$my_static . "\n"; // As of PHP 5.3.0print Bar::$my_static . "\n";$bar = new Bar();print $bar->fooStatic() . "\n";?>
