Final Keyword

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

<?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 constants example as of PHP 8.1.0

<?php
class Foo
{
    final public const 
"foo";
}

class 
Bar extends Foo
{
    public const 
"bar";
}

// Fatal error: Bar::X cannot override final constant Foo::X
?>

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.

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