Declaring class members or methods as static makes them accessible
without needing an instantiation of the class. A member declared as
static can not be accessed with an instantiated class object (though
a static method can).
The static declaration must be after the visibility declaration. For
compatibility with PHP 4, if no visibility
declaration is used, then the member or method will be treated
as if it was declared as public.
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.
In fact static method calls are resolved at compile
time. When using an explicit class name the method is already identified
completely and no inheritance rules apply. If the call is done by
self then self is translated to
the current class, that is the class the code belongs to. Here also no
inheritance rules apply.
Static properties cannot be accessed through the object using the arrow
operator ->.
Calling non-static methods statically generates an E_STRICT level warning.
Example 19-14. Static member 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
// $foo::my_static is not possible
print Bar::$my_static . "\n";
$bar = new Bar();
print $bar->fooStatic() . "\n";
?>
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Example 19-15. Static method example
<?php
class Foo {
public static function aStaticMethod() {
// ...
}
}
Foo::aStaticMethod();
?>
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