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

<?phpclass 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

<?phpfinal 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

<?phpclass 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: 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.