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<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision$ -->
<sect1 xml:id="language.oop5.final" xmlns="http://docbook.org/ns/docbook">
<title>Final Keyword</title>
<para>
The final keyword prevents child classes from overriding a method, property, or constant by
prefixing the definition with <literal>final</literal>. If the class
itself is being defined final then it cannot be extended.
</para>
<para>
<example>
<title>Final methods example</title>
<programlisting role="php">
<![CDATA[
<?php
class BaseClass {
public function test() {
echo "BaseClass::test() called\n";
}
final public function moreTesting() {
echo "BaseClass::moreTesting() called\n";
}
}
class ChildClass extends BaseClass {
public function moreTesting() {
echo "ChildClass::moreTesting() called\n";
}
}
// Results in Fatal error: Cannot override final method BaseClass::moreTesting()
?>
]]>
</programlisting>
</example>
</para>
<para>
<example>
<title>Final class example</title>
<programlisting role="php">
<![CDATA[
<?php
final class BaseClass {
public function test() {
echo "BaseClass::test() called\n";
}
// As the class is already final, the final keyword is redundant
final public function moreTesting() {
echo "BaseClass::moreTesting() called\n";
}
}
class ChildClass extends BaseClass {
}
// Results in Fatal error: Class ChildClass may not inherit from final class (BaseClass)
?>
]]>
</programlisting>
</example>
</para>
<example>
<title>Final property example as of PHP 8.4.0</title>
<programlisting role="php">
<![CDATA[
<?php
class BaseClass {
final protected string $test;
}
class ChildClass extends BaseClass {
public string $test;
}
// Results in Fatal error: Cannot override final property BaseClass::$test
?>
]]>
</programlisting>
</example>
<example xml:id="language.oop5.final.example.php81">
<title>Final constants example as of PHP 8.1.0</title>
<programlisting role="php">
<![CDATA[
<?php
class Foo
{
final public const X = "foo";
}
class Bar extends Foo
{
public const X = "bar";
}
// Fatal error: Bar::X cannot override final constant Foo::X
?>
]]>
</programlisting>
</example>
<note>
<simpara>
As of PHP 8.0.0, private methods may not be declared final except for the <link linkend="language.oop5.decon.constructor">constructor</link>.
</simpara>
</note>
<note>
<simpara>
A property that is declared <link linkend="language.oop5.visibility-members-aviz"><literal>private(set)</literal></link> is implicitly <literal>final</literal>.
</simpara>
</note>
</sect1>
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