language.oop.html

php的帮助文档,涉及到PHP的案例和基本语法,以及实际应用内容

   </p>
 
   <div class="informalexample">
    <div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB">&lt;?php<br />$cart&nbsp;</span><span style="color: #007700">=&nbsp;new&nbsp;</span><span style="color: #0000BB">Cart</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">$cart</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">add_item</span><span style="color: #007700">(</span><span style="color: #DD0000">"10"</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">1</span><span style="color: #007700">);<br /><br /></span><span style="color: #0000BB">$another_cart&nbsp;</span><span style="color: #007700">=&nbsp;new&nbsp;</span><span style="color: #0000BB">Cart</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">$another_cart</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">add_item</span><span style="color: #007700">(</span><span style="color: #DD0000">"0815"</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">3</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">?&gt;</span>
</span>
</code></div>
    </div>

   </div>
 
   <p class="para">
    This creates the objects <var class="varname">$cart</var> and
    <var class="varname">$another_cart</var>, both of the class Cart. The function
    add_item() of the <var class="varname">$cart</var> object is being called to add 1
    item of article number 10 to the <var class="varname">$cart</var>. 3 items of
    article number 0815 are being added to <var class="varname">$another_cart</var>.
   </p>
   
   <p class="para">
    Both, <var class="varname">$cart</var> and <var class="varname">$another_cart</var>, have
    functions add_item(), remove_item() and a variable items. These are
    distinct functions and variables. You can think of the objects as
    something similar to directories in a filesystem. In a filesystem you can
    have two different files <var class="filename">README.TXT</var>, as long as they
    are in different directories.  Just like with directories where you&#039;ll have
    to type the full pathname in order to reach each file from the toplevel
    directory, you have to specify the complete name of the function you want to
    call: in PHP terms, the toplevel directory would be the global namespace,
    and the pathname separator would be <i>-&gt;</i>.  Thus, the
    names <var class="varname">$cart->items</var> and
    <var class="varname">$another_cart->items</var> name two different variables.
    Note that the variable is named <var class="varname">$cart->items</var>, not
    <var class="varname">$cart->$items</var>, that is, a variable name in PHP has
    only a single dollar sign.
   </p>

   <div class="informalexample">
    <div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB">&lt;?php<br /></span><span style="color: #FF8000">//&nbsp;correct,&nbsp;single&nbsp;$<br /></span><span style="color: #0000BB">$cart</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">items&nbsp;</span><span style="color: #007700">=&nbsp;array(</span><span style="color: #DD0000">"10"&nbsp;</span><span style="color: #007700">=&gt;&nbsp;</span><span style="color: #0000BB">1</span><span style="color: #007700">);&nbsp;<br /><br /></span><span style="color: #FF8000">//&nbsp;invalid,&nbsp;because&nbsp;$cart-&gt;$items&nbsp;becomes&nbsp;$cart-&gt;""<br /></span><span style="color: #0000BB">$cart</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">$items&nbsp;</span><span style="color: #007700">=&nbsp;array(</span><span style="color: #DD0000">"10"&nbsp;</span><span style="color: #007700">=&gt;&nbsp;</span><span style="color: #0000BB">1</span><span style="color: #007700">);<br /><br /></span><span style="color: #FF8000">//&nbsp;correct,&nbsp;but&nbsp;may&nbsp;or&nbsp;may&nbsp;not&nbsp;be&nbsp;what&nbsp;was&nbsp;intended:<br />//&nbsp;$cart-&gt;$myvar&nbsp;becomes&nbsp;$cart-&gt;items<br /></span><span style="color: #0000BB">$myvar&nbsp;</span><span style="color: #007700">=&nbsp;</span><span style="color: #DD0000">'items'</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">$cart</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">$myvar&nbsp;</span><span style="color: #007700">=&nbsp;array(</span><span style="color: #DD0000">"10"&nbsp;</span><span style="color: #007700">=&gt;&nbsp;</span><span style="color: #0000BB">1</span><span style="color: #007700">);&nbsp;&nbsp;<br /></span><span style="color: #0000BB">?&gt;</span>
</span>
</code></div>
    </div>

   </div>

   <p class="para">
    Within a class definition, you do not know under which name the object
    will be accessible in your program: at the time the Cart class was
    written, it was unknown whether the object would be named
    <var class="varname">$cart</var>, <var class="varname">$another_cart</var>, or something
    else later. Thus,
    you cannot write <var class="varname">$cart->items</var> within the Cart class
    itself. Instead, in order to be able to access its own functions and
    variables from within a class, one can use the pseudo-variable
    <var class="varname">$this</var> which can be read as &#039;my own&#039; or &#039;current
    object&#039;. Thus, &#039;<var class="varname">$this->items[$artnr]</var> +=
    <var class="varname">$num</var>&#039; can be read as &#039;add <var class="varname">$num</var> to
    the <var class="varname">$artnr</var> counter of my own items array&#039; or &#039;add
    <var class="varname">$num</var> to the <var class="varname">$artnr</var> counter of the
    items array within the current object&#039;.
   </p>

   <blockquote><p><b class="note">Note</b>: 
    
     The <var class="varname">$this</var> pseudo-variable is not usually defined if
     the method in which it is hosted is called statically. This is not,
     however, a strict rule: <var class="varname">$this</var> is defined if a method is
     called statically from within another object. In this case, the value of
     <var class="varname">$this</var> is that of the calling object. This is
     illustrated in the following example:
     <div class="informalexample">
      <div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB">&lt;?php<br /></span><span style="color: #007700">class&nbsp;</span><span style="color: #0000BB">A<br /></span><span style="color: #007700">{<br />&nbsp;&nbsp;&nbsp;&nbsp;function&nbsp;</span><span style="color: #0000BB">foo</span><span style="color: #007700">()<br />&nbsp;&nbsp;&nbsp;&nbsp;{<br />&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if&nbsp;(isset(</span><span style="color: #0000BB">$this</span><span style="color: #007700">))&nbsp;{<br />&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;echo&nbsp;</span><span style="color: #DD0000">'$this&nbsp;is&nbsp;defined&nbsp;('</span><span style="color: #007700">;<br />&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;echo&nbsp;</span><span style="color: #0000BB">get_class</span><span style="color: #007700">(</span><span style="color: #0000BB">$this</span><span style="color: #007700">);<br />&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;echo&nbsp;</span><span style="color: #DD0000">")\n"</span><span style="color: #007700">;<br />&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}&nbsp;else&nbsp;{<br />&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;echo&nbsp;</span><span style="color: #DD0000">"\$this&nbsp;is&nbsp;not&nbsp;defined.\n"</span><span style="color: #007700">;<br />&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}<br />&nbsp;&nbsp;&nbsp;&nbsp;}<br />}<br /><br />class&nbsp;</span><span style="color: #0000BB">B<br /></span><span style="color: #007700">{<br />&nbsp;&nbsp;&nbsp;&nbsp;function&nbsp;</span><span style="color: #0000BB">bar</span><span style="color: #007700">()<br />&nbsp;&nbsp;&nbsp;&nbsp;{<br />&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span style="color: #0000BB">A</span><span style="color: #007700">::</span><span style="color: #0000BB">foo</span><span style="color: #007700">();<br />&nbsp;&nbsp;&nbsp;&nbsp;}<br />}<br /><br /></span><span style="color: #0000BB">$a&nbsp;</span><span style="color: #007700">=&nbsp;new&nbsp;</span><span style="color: #0000BB">A</span><span style="color: #007700">();<br /></span><span style="color: #0000BB">$a</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">foo</span><span style="color: #007700">();<br /></span><span style="color: #0000BB">A</span><span style="color: #007700">::</span><span style="color: #0000BB">foo</span><span style="color: #007700">();<br /></span><span style="color: #0000BB">$b&nbsp;</span><span style="color: #007700">=&nbsp;new&nbsp;</span><span style="color: #0000BB">B</span><span style="color: #007700">();<br /></span><span style="color: #0000BB">$b</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">bar</span><span style="color: #007700">();<br /></span><span style="color: #0000BB">B</span><span style="color: #007700">::</span><span style="color: #0000BB">bar</span><span style="color: #007700">();<br /></span><span style="color: #0000BB">?&gt;</span>
</span>
</code></div>     
      </div>

      <p class="para">The above example will output:</p>
      <div class="example-contents"><pre>
<div class="cdata"><pre>
$this is defined (a)
$this is not defined.
$this is defined (b)
$this is not defined.
</pre></div>
      </pre></div>
     </div>
    <br />
   </p></blockquote>

   <blockquote><p><b class="note">Note</b>: 
    
    There are some nice functions to handle classes and objects. You might want
    to take a look at the <a href="ref.classobj.html" class="link">Class/Object
    Functions</a>.
    <br />
   </p></blockquote>
  </div>
  
  

  

 

 

 

 
  
 

  
 </div>
<hr /><div style="text-align: center;">
 <div class="prev" style="text-align: left; float: left;"><a href="functions.internal.html">Internal (built-in) functions</a></div>
 <div class="next" style="text-align: right; float: right;"><a href="keyword.extends.html">extends</a></div>
 <div class="up"><a href="langref.html">Language Reference</a></div>
 <div class="home"><a href="index.html">PHP Manual</a></div>
</div></body></html>