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<?xml version="1.0" encoding="iso-8859-1"?>
<!-- $Revision: 1.9 $ -->
<sect1 id="language.oop5.static">
<title>Static Keyword</title>
<para>
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).
</para>
<para>
The static declaration must be after the visibility declaration. For
compatibility with PHP 4, if no <link
linkend="language.oop5.visibility">visibility</link>
declaration is used, then the member or method will be treated
as if it was declared as <literal>public</literal>.
</para>
<para>
Because static methods are callable without an instance of
the object created, the pseudo variable <varname>$this</varname> is
not available inside the method declared as static.
</para>
<para>
In fact <literal>static</literal> 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
<literal>self</literal> then <literal>self</literal> is translated to
the current class, that is the class the code belongs to. Here also no
inheritance rules apply.
</para>
<para>
Static properties cannot be accessed through the object using the arrow
operator ->.
</para>
<para>
Calling non-static methods statically generates an E_STRICT level warning.
</para>
<example>
<title>Static member example</title>
<programlisting role="php">
<![CDATA[
<?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";
?>
]]>
</programlisting>
</example>
<example>
<title>Static method example</title>
<programlisting role="php">
<![CDATA[
<?php
class Foo {
public static function aStaticMethod() {
// ...
}
}
Foo::aStaticMethod();
?>
]]>
</programlisting>
</example>
</sect1>
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