<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
<title>Object Inheritance</title>
</head>
<body><div class="manualnavbar" style="text-align: center;">
<div class="prev" style="text-align: left; float: left;"><a href="language.oop5.visibility.html">Visibility</a></div>
<div class="next" style="text-align: right; float: right;"><a href="language.oop5.paamayim-nekudotayim.html">Scope Resolution Operator (::)</a></div>
<div class="up"><a href="language.oop5.html">Classes and Objects</a></div>
<div class="home"><a href="index.html">PHP Manual</a></div>
</div><hr /><div id="language.oop5.inheritance" class="sect1">
<h2 class="title">Object Inheritance</h2>
<p class="para">
Inheritance is a well-established programming principle, and PHP makes use
of this principle in its object model. This principle will affect the way
many classes and objects relate to one another.
</p>
<p class="para">
For example, when you extend a class, the subclass inherits all of the
public and protected methods from the parent class. Unless a class overrides
those methods, they will retain their original functionality.
</p>
<p class="para">
This is useful for defining and abstracting functionality, and permits the
implementation of additional functionality in similar objects without the
need to reimplement all of the shared functionality.
</p>
<blockquote class="note"><p><strong class="note">Note</strong>:
<p class="para">
Unless autoloading is used, then classes must be defined before they are
used. If a class extends another, then the parent class must be declared
before the child class structure. This rule applies to classes that inherit
other classes and interfaces.
</p>
</p></blockquote>
<div class="sect2" id="language.oop5.inheritance.examples">
<div class="example" id="language.oop5.inheritance.examples.ex1">
<p><strong>Example #1 Inheritance Example</strong></p>
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /><br /></span><span style="color: #007700">class </span><span style="color: #0000BB">foo<br /></span><span style="color: #007700">{<br /> public function </span><span style="color: #0000BB">printItem</span><span style="color: #007700">(</span><span style="color: #0000BB">$string</span><span style="color: #007700">)<br /> {<br /> echo </span><span style="color: #DD0000">'Foo: ' </span><span style="color: #007700">. </span><span style="color: #0000BB">$string </span><span style="color: #007700">. </span><span style="color: #0000BB">PHP_EOL</span><span style="color: #007700">;<br /> }<br /> <br /> public function </span><span style="color: #0000BB">printPHP</span><span style="color: #007700">()<br /> {<br /> echo </span><span style="color: #DD0000">'PHP is great.' </span><span style="color: #007700">. </span><span style="color: #0000BB">PHP_EOL</span><span style="color: #007700">;<br /> }<br />}<br /><br />class </span><span style="color: #0000BB">bar </span><span style="color: #007700">extends </span><span style="color: #0000BB">foo<br /></span><span style="color: #007700">{<br /> public function </span><span style="color: #0000BB">printItem</span><span style="color: #007700">(</span><span style="color: #0000BB">$string</span><span style="color: #007700">)<br /> {<br /> echo </span><span style="color: #DD0000">'Bar: ' </span><span style="color: #007700">. </span><span style="color: #0000BB">$string </span><span style="color: #007700">. </span><span style="color: #0000BB">PHP_EOL</span><span style="color: #007700">;<br /> }<br />}<br /><br /></span><span style="color: #0000BB">$foo </span><span style="color: #007700">= new </span><span style="color: #0000BB">foo</span><span style="color: #007700">();<br /></span><span style="color: #0000BB">$bar </span><span style="color: #007700">= new </span><span style="color: #0000BB">bar</span><span style="color: #007700">();<br /></span><span style="color: #0000BB">$foo</span><span style="color: #007700">-></span><span style="color: #0000BB">printItem</span><span style="color: #007700">(</span><span style="color: #DD0000">'baz'</span><span style="color: #007700">); </span><span style="color: #FF8000">// Output: 'Foo: baz'<br /></span><span style="color: #0000BB">$foo</span><span style="color: #007700">-></span><span style="color: #0000BB">printPHP</span><span style="color: #007700">(); </span><span style="color: #FF8000">// Output: 'PHP is great' <br /></span><span style="color: #0000BB">$bar</span><span style="color: #007700">-></span><span style="color: #0000BB">printItem</span><span style="color: #007700">(</span><span style="color: #DD0000">'baz'</span><span style="color: #007700">); </span><span style="color: #FF8000">// Output: 'Bar: baz'<br /></span><span style="color: #0000BB">$bar</span><span style="color: #007700">-></span><span style="color: #0000BB">printPHP</span><span style="color: #007700">(); </span><span style="color: #FF8000">// Output: 'PHP is great'<br /><br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
</div>
</div><hr /><div class="manualnavbar" style="text-align: center;">
<div class="prev" style="text-align: left; float: left;"><a href="language.oop5.visibility.html">Visibility</a></div>
<div class="next" style="text-align: right; float: right;"><a href="language.oop5.paamayim-nekudotayim.html">Scope Resolution Operator (::)</a></div>
<div class="up"><a href="language.oop5.html">Classes and Objects</a></div>
<div class="home"><a href="index.html">PHP Manual</a></div>
</div></body></html>
