6.7.4 FinalThis is NOT the latest copy of this book; click here for the latest version.
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)".
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