Final Keyword

PHP 5 introduces the final keyword, which prevents child classes from overriding a method by prefixing the definition with final. If the class itself is being defined final then it cannot be extended.

例 19-29. 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()
?>

例 19-30. Final class example


<?php
final class BaseClass {
   public function test() {
       echo "BaseClass::test() called\n";
   }

   // Here it doesn't matter if you specify the function as final or not
   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)
?>

add a note User Contributed Notes

penartur at yandex dot ru
22-Mar-2007 09:39


Note that you cannot ovverride final methods even if they are defined as private in parent class.

Thus, the following example:

<?php

class parentClass {

    final private function someMethod() { }

}

class childClass extends parentClass {

    private function someMethod() { }

}

?>

dies with error "Fatal error: Cannot override final method parentClass::someMethod() in ***.php on line 7"



Such behaviour looks slight unexpected because in child class we cannot know, which private methods exists in a parent class and vice versa.



So, remember that if you defined a private static method, you cannot place method with the same name in child class.

liumr at ustc dot edu
11-Mar-2007 06:29


this key word can describe a class or a class member function

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