Final

The final keyword is used to declare that a function or class cannot be overriden by a sub-class. This is another way of stopping other programmers using your code outside the bounds you had planned for it.

Take a look at the following code:

class dog {

      private $Name;

      private $DogTag;

      final public function bark() {

          print "Woof!\n";

      }

The dog bark() function is now declared as being final, which means it cannot be overridden in a child class. If we have bark() redefined in the poodle class, PHP outputs a fatal error message: Cannot override final method dog::bark(). Using the final keyword is entirely optional, but it makes your life easier by acting as a safeguard against people overriding a function you believe should be permanent.

For stronger protection, the final keyword can also be used to declare a class as uninheritable - that is, that programmers cannot extend another class from it. Take a look at this script:

<?php

      final class dog {

          public $Name;

          private function getName() {

              return $this->Name;

          }

      }

  

      class poodle extends dog {

          public function bark() {

              print "'Woof', says " . $this->getName();

          }

      }
 ?>

Attempting to run that script will result in a fatal error, with the message "Class poodle may not inherit from final class (dog)".

Next chapter: Abstract >>

Previous chapter: Protected

Jump to:

Home: Table of Contents