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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"><html> <head> <title>Class Abstraction</title> <meta http-equiv="content-type" content="text/html; charset=UTF-8"> </head> <body><div style="text-align: center;"> <div class="prev" style="text-align: left; float: left;"><a href="language.oop5.constants.html">Class Constants</a></div> <div class="next" style="text-align: right; float: right;"><a href="language.oop5.interfaces.html">Object Interfaces</a></div> <div class="up"><a href="language.oop5.html">Classes and Objects (PHP 5)</a></div> <div class="home"><a href="index.html">PHP Manual</a></div></div><hr /><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.html" 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"><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">$prefix</span><span style="color: #007700">) {<br /> return </span><span style="color: #DD0000">"{$prefix}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">$prefix</span><span style="color: #007700">) {<br /> return </span><span style="color: #DD0000">"{$prefix}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"><p>The above example will output:</p></div> <div class="example-contents"><pre><div class="cdata"><pre>ConcreteClass1FOO_ConcreteClass1ConcreteClass2FOO_ConcreteClass2</pre></div> </pre></div> </div> <p class="para"> Old code that has no user-defined classes or functions named 'abstract' should run without modifications. </p> </div><hr /><div style="text-align: center;"> <div class="prev" style="text-align: left; float: left;"><a href="language.oop5.constants.html">Class Constants</a></div> <div class="next" style="text-align: right; float: right;"><a href="language.oop5.interfaces.html">Object Interfaces</a></div> <div class="up"><a href="language.oop5.html">Classes and Objects (PHP 5)</a></div> <div class="home"><a href="index.html">PHP Manual</a></div></div></body></html>⌨️ 快捷键说明
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