Final Keyword
The final keyword prevents child classes from overriding a method or constant by prefixing the definition with final
. If the class itself is being defined final then it cannot be extended.
Example #1 Final methods example
<?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() ?>
Example #2 Final class example
<?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) ?>
Example #3 Final constants example as of PHP 8.1.0
<?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 ?>
Note: Properties cannot be declared final: only classes, methods, and constants (as of PHP 8.1.0) may be declared as final. As of PHP 8.0.0, private methods may not be declared final except for the constructor.
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https://www.php.net/manual/en/language.oop5.final.php