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>章 19. 类与对象（PHP 5）</TD
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><P
> 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).
</P
><P
> The static declaration must be after the visibility declaration. For
compatibility with PHP 4, if no <A
HREF="language.oop5.visibility.html"
>visibility</A
>
declaration is used, then the member or method will be treated
as if it was declared as <TT
CLASS="literal"
>public</TT
>.
</P
><P
> Because static methods are callable without an instance of
the object created, the pseudo variable <CODE
CLASS="varname"
>$this</CODE
> is
not available inside the method declared as static.
</P
><P
> In fact <TT
CLASS="literal"
>static</TT
> method calls are resolved at compile
time. When using an explicit class name the method is already identified
completely and no inheritance rules apply. If the call is done by
<TT
CLASS="literal"
>self</TT
> then <TT
CLASS="literal"
>self</TT
> is translated to
the current class, that is the class the code belongs to. Here also no
inheritance rules apply.
</P
><P
> Static properties cannot be accessed through the object using the arrow
operator ->.
</P
><P
> Calling non-static methods statically generates an E_STRICT level warning.
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>例 19-15. Static member example</B
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><code><font color="#000000">
<font color="#0000BB"><?php<br /></font><font color="#007700">class </font><font color="#0000BB">Foo<br /></font><font color="#007700">{<br /> </font><font color="#0000BB">public </font><font color="#007700">static </font><font color="#0000BB">$my_static </font><font color="#007700">= </font><font color="#DD0000">'foo'</font><font color="#007700">;<br /><br /> </font><font color="#0000BB">public </font><font color="#007700">function </font><font color="#0000BB">staticValue</font><font color="#007700">() {<br /> return </font><font color="#0000BB">self</font><font color="#007700">::</font><font color="#0000BB">$my_static</font><font color="#007700">;<br /> }<br />}<br /><br />class </font><font color="#0000BB">Bar </font><font color="#007700">extends </font><font color="#0000BB">Foo<br /></font><font color="#007700">{<br /> </font><font color="#0000BB">public </font><font color="#007700">function </font><font color="#0000BB">fooStatic</font><font color="#007700">() {<br /> return </font><font color="#0000BB">parent</font><font color="#007700">::</font><font color="#0000BB">$my_static</font><font color="#007700">;<br /> }<br />}<br /><br /><br />print </font><font color="#0000BB">Foo</font><font color="#007700">::</font><font color="#0000BB">$my_static </font><font color="#007700">. </font><font color="#DD0000">"\n"</font><font color="#007700">;<br /><br /></font><font color="#0000BB">$foo </font><font color="#007700">= new </font><font color="#0000BB">Foo</font><font color="#007700">();<br />print </font><font color="#0000BB">$foo</font><font color="#007700">-></font><font color="#0000BB">staticValue</font><font color="#007700">() . </font><font color="#DD0000">"\n"</font><font color="#007700">;<br />print </font><font color="#0000BB">$foo</font><font color="#007700">-></font><font color="#0000BB">my_static </font><font color="#007700">. </font><font color="#DD0000">"\n"</font><font color="#007700">; </font><font color="#FF8000">// Undefined "Property" my_static <br /><br />// $foo::my_static is not possible<br /><br /></font><font color="#007700">print </font><font color="#0000BB">Bar</font><font color="#007700">::</font><font color="#0000BB">$my_static </font><font color="#007700">. </font><font color="#DD0000">"\n"</font><font color="#007700">;<br /></font><font color="#0000BB">$bar </font><font color="#007700">= new </font><font color="#0000BB">Bar</font><font color="#007700">();<br />print </font><font color="#0000BB">$bar</font><font color="#007700">-></font><font color="#0000BB">fooStatic</font><font color="#007700">() . </font><font color="#DD0000">"\n"</font><font color="#007700">;<br /></font><font color="#0000BB">?></font>
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><P
><B
>例 19-16. Static method example</B
></P
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><code><font color="#000000">
<font color="#0000BB"><?php<br /></font><font color="#007700">class </font><font color="#0000BB">Foo </font><font color="#007700">{<br /> </font><font color="#0000BB">public </font><font color="#007700">static function </font><font color="#0000BB">aStaticMethod</font><font color="#007700">() {<br /> </font><font color="#FF8000">// ...<br /> </font><font color="#007700">}<br />}<br /><br /></font><font color="#0000BB">Foo</font><font color="#007700">::</font><font color="#0000BB">aStaticMethod</font><font color="#007700">();<br /></font><font color="#0000BB">?></font>
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