PHP Manual: Static Keyword

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, define static anonymous functions 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. These can also be accessed statically within an instantiated class object.

Static methods

Because static methods are callable without an instance of the object created, the pseudo-variable $this is not available inside methods declared as static.

Warning

Calling non-static methods statically throws an Error.

Prior to PHP 8.0.0, calling non-static methods statically were deprecated, and generated an E_DEPRECATED warning.

Example #1 Static method example

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

Foo::aStaticMethod();
$classname = 'Foo';
$classname::aStaticMethod();
?>

Static properties

Static properties are accessed using the Scope Resolution Operator (::) and cannot be accessed through the object operator (->).

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

<?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";      // Undefined "Property" my_static 

print $foo::$my_static . "\n";
$classname = 'Foo';
print $classname::$my_static . "\n";

print Bar::$my_static . "\n";
$bar = new Bar();
print $bar->fooStatic() . "\n";
?>

Output of the above example in PHP 8 is similar to:

foo
foo

Notice: Accessing static property Foo::$my_static as non static in /in/V0Rvv on line 23

Warning: Undefined property: Foo::$my_static in /in/V0Rvv on line 23

foo
foo
foo
foo