What is a final class in php?

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

Example #2 Final class example

Example #3 Final constants example as of PHP 8.1.0

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.

penartur at yandex dot ru ¶

15 years ago

Note that you cannot ovverride final methods even if they are defined as private in parent class.
Thus, the following example:

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 final method, you cannot place method with the same name in child class.

someone dot else at elsewhere dot net ¶

8 years ago

@thomas at somewhere dot com

The 'final' keyword is extremely useful.  Inheritance is also useful, but can be abused and becomes problematic in large applications.  If you ever come across a finalized class or method that you wish to extend, write a decorator instead.

mattsch at gmail dot com ¶

8 years ago

You can use final methods to replace class constants.  The reason for this is you cannot unit test a class constant used in another class in isolation because you cannot mock a constant.   Final methods allow you to have the same functionality as a constant while keeping your code loosely coupled.

Tight coupling example [bad to use constants]:



Loose coupling example [eliminated constant usage]:

cottton at i-stats dot net ¶

8 years ago

imo good to know:


santoshjoshi2003 at yahoo dot co dot in ¶

13 years ago

The use of final keyword is just like that occurs in Java
In java final has three uses
    1] prevent class Inheritance
    2] prevent method overriding or redifination of
        method in subclass
    3] and to declare constants
But the third point seems to be missing from the PHP
I guess, as i am a java developer Currently gaining competence in PHP

Anonymous ¶

11 years ago

The behaviour of FINAL is not as serious as you may think. A little explample:


Normally you would expect some of the following will happen:
- An error that final and private keyword cannot be used together
- No error as the private visibility says, that a method/var/etc. is only visible within the same class

But what happens is PHP is a little curios: "Cannot override final method A::method[]"

So its possible to deny method names in subclasses! Don't know if this is  a good behavior, but maybe its useful for your purpose.

Baldurien ¶

12 years ago

"Note for Java developers: the 'final' keyword is not used for class constants in PHP. We use the keyword 'const'."

//php.net/manual/en/language.oop5.constants.php

This is more or less true, regardless of the fact that constant [being defined at class level or not] in PHP are only scalar [int, string, etc] while in Java they may be pure object [ex: java.awat.Color.BLACK]. The only possible solution of having such kind of constant is :


That said, perhaps it is useless unless PHP automatically calls the __init[] method.

However, one alternative that could be done in certain case is this :



This can only work when one class is defined per file, since we are assured that __autoload[] will be called to load the file containing the class.

eg:

test2.php:

test.php:


slorenzo at clug dot org dot ve ¶

14 years ago

t at bestcodepractise dot com ¶

8 years ago

@someone
@thomas
Decorating a finalized class is not possible. The decorator that's mentioned is incomplete. There's a fundamental flaw in it. Look:

What you've created is just an object that happens to have the same methods[a duck type]. But if in the client code someone makes decision based on the type of your passed decorator they'll make incorrect decision - or to be more precise not the one that you, the author of the 'decorator' wants them to make.
FYI that's the correct implementation based on GoF:


I haven't come across any legitimate use of a finalizing class/method and I personally think that 'final' is has no much use and is just a copy'n'pasted from Java into PHP. The keyword makes code difficult to test. If you have to create a test double from a finalized class because you'll need create a derived type to shadow the methods you don't care about. If one of them is finalized you've already lost.

xavier dot inghels at gmail dot com ¶

7 years ago

Final is not really about overriding or overloading a method.
PHP doesn't support [yet ?] method ovverriding.

The final keyword however prevent you to redefine a method already previously declared.

suisuiruyi at gmail dot com ¶

6 years ago

Note: Properties cannot be declared final, only classes and methods may be declared as final.
you can use trait:


John smith ¶

5 years ago

Right way:
final protected function example[] {
}

Wrong way:

protected final function example[] {
}

Source: Practices