Source of: /manual/en/language.oop5.abstract.php
<?php
include_once $_SERVER['DOCUMENT_ROOT'] . '/include/shared-manual.inc';
$TOC = array();
$PARENTS = array();
include_once dirname(__FILE__) ."/toc/language.oop5.inc";
$setup = array (
'home' =>
array (
0 => 'index.php',
1 => 'PHP Manual',
),
'head' =>
array (
0 => 'UTF-8',
1 => 'en',
),
'this' =>
array (
0 => 'language.oop5.abstract.php',
1 => 'Class Abstraction',
),
'up' =>
array (
0 => 'language.oop5.php',
1 => 'Classes and Objects',
),
'prev' =>
array (
0 => 'language.oop5.static.php',
1 => 'Static Keyword',
),
'next' =>
array (
0 => 'language.oop5.interfaces.php',
1 => 'Object Interfaces',
),
);
$setup["toc"] = $TOC;
$setup["parents"] = $PARENTS;
manual_setup($setup);
manual_header();
?>
<div id="language.oop5.abstract" class="sect1">
<h2 class="title">Class Abstraction</h2>
<p class="para">
PHP 5 introduces abstract classes and methods. It is not allowed to create
an instance of a class that has been defined as abstract. Any class that
contains at least one abstract method must also be abstract. Methods
defined as abstract simply declare the method's signature they cannot
define the implementation.
</p>
<p class="para">
When inheriting from an abstract class, all methods marked abstract in
the parent's class declaration must be defined by the child; additionally,
these methods must be defined with the same (or a less restricted)
<a href="language.oop5.visibility.php" class="link">visibility</a>. For example,
if the abstract method is defined as protected, the function implementation
must be defined as either protected or public, but not private.
</p>
<div class="example">
<p><b>Example #1 Abstract class example</b></p>
<div class="example-contents programlisting">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /></span><span style="color: #007700">abstract class </span><span style="color: #0000BB">AbstractClass<br /></span><span style="color: #007700">{<br /> </span><span style="color: #FF8000">// Force Extending class to define this method<br /> </span><span style="color: #007700">abstract protected function </span><span style="color: #0000BB">getValue</span><span style="color: #007700">();<br /> abstract protected function </span><span style="color: #0000BB">prefixValue</span><span style="color: #007700">(</span><span style="color: #0000BB">$prefix</span><span style="color: #007700">);<br /><br /> </span><span style="color: #FF8000">// Common method<br /> </span><span style="color: #007700">public function </span><span style="color: #0000BB">printOut</span><span style="color: #007700">() {<br /> print </span><span style="color: #0000BB">$this</span><span style="color: #007700">-></span><span style="color: #0000BB">getValue</span><span style="color: #007700">() . </span><span style="color: #DD0000">"\n"</span><span style="color: #007700">;<br /> }<br />}<br /><br />class </span><span style="color: #0000BB">ConcreteClass1 </span><span style="color: #007700">extends </span><span style="color: #0000BB">AbstractClass<br /></span><span style="color: #007700">{<br /> protected function </span><span style="color: #0000BB">getValue</span><span style="color: #007700">() {<br /> return </span><span style="color: #DD0000">"ConcreteClass1"</span><span style="color: #007700">;<br /> }<br /><br /> public function </span><span style="color: #0000BB">prefixValue</span><span style="color: #007700">(</span><span style="color: #0000BB">$prefix</span><span style="color: #007700">) {<br /> return </span><span style="color: #DD0000">"</span><span style="color: #007700">{</span><span style="color: #0000BB">$prefix</span><span style="color: #007700">}</span><span style="color: #DD0000">ConcreteClass1"</span><span style="color: #007700">;<br /> }<br />}<br /><br />class </span><span style="color: #0000BB">ConcreteClass2 </span><span style="color: #007700">extends </span><span style="color: #0000BB">AbstractClass<br /></span><span style="color: #007700">{<br /> public function </span><span style="color: #0000BB">getValue</span><span style="color: #007700">() {<br /> return </span><span style="color: #DD0000">"ConcreteClass2"</span><span style="color: #007700">;<br /> }<br /><br /> public function </span><span style="color: #0000BB">prefixValue</span><span style="color: #007700">(</span><span style="color: #0000BB">$prefix</span><span style="color: #007700">) {<br /> return </span><span style="color: #DD0000">"</span><span style="color: #007700">{</span><span style="color: #0000BB">$prefix</span><span style="color: #007700">}</span><span style="color: #DD0000">ConcreteClass2"</span><span style="color: #007700">;<br /> }<br />}<br /><br /></span><span style="color: #0000BB">$class1 </span><span style="color: #007700">= new </span><span style="color: #0000BB">ConcreteClass1</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">$class1</span><span style="color: #007700">-></span><span style="color: #0000BB">printOut</span><span style="color: #007700">();<br />echo </span><span style="color: #0000BB">$class1</span><span style="color: #007700">-></span><span style="color: #0000BB">prefixValue</span><span style="color: #007700">(</span><span style="color: #DD0000">'FOO_'</span><span style="color: #007700">) .</span><span style="color: #DD0000">"\n"</span><span style="color: #007700">;<br /><br /></span><span style="color: #0000BB">$class2 </span><span style="color: #007700">= new </span><span style="color: #0000BB">ConcreteClass2</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">$class2</span><span style="color: #007700">-></span><span style="color: #0000BB">printOut</span><span style="color: #007700">();<br />echo </span><span style="color: #0000BB">$class2</span><span style="color: #007700">-></span><span style="color: #0000BB">prefixValue</span><span style="color: #007700">(</span><span style="color: #DD0000">'FOO_'</span><span style="color: #007700">) .</span><span style="color: #DD0000">"\n"</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
<div class="example-contents para"><p>The above example will output:</p></div>
<div class="example-contents screen">
<div class="cdata"><pre>
ConcreteClass1
FOO_ConcreteClass1
ConcreteClass2
FOO_ConcreteClass2
</pre></div>
</div>
</div>
<p class="para">
Old code that has no user-defined classes or functions named
'abstract' should run without modifications.
</p>
</div><?php manual_footer(); ?>
