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https://github.com/php/doc-zh.git
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133 lines
3.1 KiB
XML
133 lines
3.1 KiB
XML
<?xml version="1.0" encoding="utf-8"?>
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<!-- $Revision$ -->
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<!-- EN-Revision: 16f66c05a4060a7d673ae1c70b656d65009407b0 Maintainer: Haohappy Status: ready -->
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<!-- CREDITS: Luffy -->
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<sect1 xml:id="language.oop5.final" xmlns="http://docbook.org/ns/docbook">
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<title>Final 关键字</title>
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<para>
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final 关键字通过在定义方法、属性和常量之前加上 <literal>final</literal> 来防止被子类覆盖。
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如果一个类被声明为 final，则不能被继承。
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</para>
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<para>
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<example>
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<title>Final 方法示例</title>
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<programlisting role="php">
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<![CDATA[
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<?php
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class BaseClass {
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public function test() {
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echo "BaseClass::test() called\n";
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}
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final public function moreTesting() {
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echo "BaseClass::moreTesting() called\n";
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}
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}
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class ChildClass extends BaseClass {
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public function moreTesting() {
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echo "ChildClass::moreTesting() called\n";
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}
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}
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// 产生 Fatal error: Cannot override final method BaseClass::moreTesting()
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?>
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]]>
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</programlisting>
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</example>
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</para>
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<para>
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<example>
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<title>Final 类示例</title>
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<programlisting role="php">
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<![CDATA[
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<?php
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final class BaseClass {
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public function test() {
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echo "BaseClass::test() called\n";
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}
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// 由于类已经是 final，所以 final 关键字是多余的
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final public function moreTesting() {
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echo "BaseClass::moreTesting() called\n";
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}
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}
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class ChildClass extends BaseClass {
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}
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// 产生 Fatal error: Class ChildClass may not inherit from final class (BaseClass)
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?>
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]]>
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</programlisting>
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</example>
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</para>
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<example>
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<title>PHP 8.4.0 起可用的 final 属性示例</title>
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<programlisting role="php">
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<![CDATA[
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<?php
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class BaseClass {
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final protected string $test;
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}
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class ChildClass extends BaseClass {
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public string $test;
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}
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// Results in Fatal error: Cannot override final property BaseClass::$test
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?>
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]]>
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</programlisting>
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</example>
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<example xml:id="language.oop5.final.example.php81">
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<title>PHP 8.1.0 起可用的 final 常量示例</title>
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<programlisting role="php">
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<![CDATA[
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<?php
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class Foo
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{
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final public const X = "foo";
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}
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class Bar extends Foo
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{
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public const X = "bar";
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}
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// Fatal error: Bar::X cannot override final constant Foo::X
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?>
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]]>
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</programlisting>
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</example>
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<note>
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<simpara>
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从 PHP 8.0.0 起，除了<link linkend="language.oop5.decon.constructor">构造函数</link>之外，私有方法也不能声明为 final 。
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</simpara>
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<simpara>
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声明为 <link linkend="language.oop5.visibility-members-aviz"><literal>private(set)</literal></link> 的属性是隐式的 <literal>final</literal>。
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</simpara>
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</note>
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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:"~/.phpdoc/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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