PHP: Hypertext Preprocessor (original) (raw)

Final Keyword

The final keyword prevents child classes from overriding a method, property, 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 property example as of PHP 8.4.0

`<?php
class BaseClass {
final protected string $test;
}

class

ChildClass extends BaseClass {
public string $test;
}
// Results in Fatal error: Cannot override final property BaseClass::$test
?>`

Example #4 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: As of PHP 8.0.0, private methods may not be declared final except for the constructor.

Note: A property that is declared private(set) is implicitly final.

Found A Problem?

jriddy at gmail dot com ¶

15 years ago

penartur at yandex dot ru ¶

18 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.

`

Rumour ¶

2 years ago

Class constants CAN be “finalised” since PHP8.1. To partly contradict to the most popular user contribution, that was written a long time ago, they were still absolutely right.

someone dot else at elsewhere dot net ¶

11 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.

`

slorenzo at clug dot org dot ve ¶

17 years ago

<?php class parentClass { public function someMethod() { } } class childClass extends parentClass { public final function someMethod() { } //override parent function }$class = new childClass; $class->someMethod(); //call the override function in chield class ?>

mattsch at gmail dot com ¶

10 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 ¶

10 years ago

`` imo good to know:
<?php
class BaseClass
{
protected static $var = 'i belong to BaseClass';

public static function

test()
{
echo '