Final Keyword

Def: Final Keyword prevents child classes from overriding a method by prefixing the definition with final. If the class itself is being defined final then it cannot be extended

Final Method

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()

Final Class:

final class BaseClass {
   public function test() {
       echo "BaseClass::test() called\n";
   }

   // Here it doesn't matter if you specify the function as final or not
   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)

Final constants: Unlike Java, the final keyword is not used for class constants in PHP. Use the keyword const instead.

Why do I have to use final****?

1. Preventing massive inheritance chain of doom
2. Encouraging composition
3. Force the developer to think about user public API
4. Force the developer to shrink an object’s public API
5. A final class can always be made extensible
6. extends breaks encapsulation
7. You don’t need that flexibility
8. You are free to change the code

When to avoid final****: Final classes only work effectively under following assumptions:

1. There is an abstraction (interface) that the final class implements
2. All of the public API of the final class is part of that interface