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https://github.com/sigmasternchen/php-doc-en
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git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@192322 c90b9560-bf6c-de11-be94-00142212c4b1
108 lines
2.6 KiB
XML
108 lines
2.6 KiB
XML
<?xml version="1.0" encoding="iso-8859-1"?>
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<!-- $Revision: 1.13 $ -->
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<sect1 id="language.oop5.abstract">
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<title>Class Abstraction</title>
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<para>
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PHP 5 introduces abstract classes and methods. It is not allowed to create
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an instance of a class that has been defined as abstract. Any class that
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contains at least one abstract method must also be abstract. Methods
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defined as abstract simply declare the method's signature they cannot
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define the implementation.
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</para>
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<para>
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When inheriting from an abstract class, all methods marked abstract in
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the parent's class declaration must be defined by the child; additionally,
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these methods must be defined with the same (or weaker)
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<link linkend="language.oop5.visibility">visibillity</link>. For example,
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if the abstract method is defined as protected, the function implementation
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must be defined as either protected or public.
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</para>
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<example>
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<title>Abstract class example</title>
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<programlisting role="php">
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<![CDATA[
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<?php
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abstract class AbstractClass
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{
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// Force Extending class to define this method
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abstract protected function getValue();
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abstract protected function prefixValue($prefix);
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// Common method
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public function printOut() {
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print $this->getValue() . "\n";
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}
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}
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class ConcreteClass1 extends AbstractClass
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{
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protected function getValue() {
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return "ConcreteClass1";
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}
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public function prefixValue($prefix) {
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return "{$prefix}ConcreteClass1";
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}
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}
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class ConcreteClass2 extends AbstractClass
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{
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public function getValue() {
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return "ConcreteClass2";
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}
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public function prefixValue($prefix) {
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return "{$prefix}ConcreteClass2";
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}
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}
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$class1 = new ConcreteClass1;
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$class1->printOut();
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echo $class1->prefixValue('FOO_') ."\n";
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$class2 = new ConcreteClass2;
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$class2->printOut();
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echo $class2->prefixValue('FOO_') ."\n";
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?>
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]]>
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</programlisting>
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&example.outputs;
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<screen>
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<![CDATA[
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ConcreteClass1
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FOO_ConcreteClass1
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ConcreteClass2
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FOO_ConcreteClass2
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]]>
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</screen>
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</example>
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<para>
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Old code that has no user-defined classes or functions named
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'abstract' should run without modifications.
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</para>
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</sect1>
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<!-- Keep this comment at the end of the file
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Local variables:
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mode: sgml
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sgml-omittag:t
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sgml-shorttag:t
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sgml-minimize-attributes:nil
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sgml-always-quote-attributes:t
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sgml-indent-step:1
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sgml-indent-data:t
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indent-tabs-mode:nil
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sgml-parent-document:nil
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sgml-default-dtd-file:"../../manual.ced"
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sgml-exposed-tags:nil
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sgml-local-catalogs:nil
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sgml-local-ecat-files:nil
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End:
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vim600: syn=xml fen fdm=syntax fdl=2 si
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vim: et tw=78 syn=sgml
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vi: ts=1 sw=1
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-->
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