Object-oriented programming in PHP gives developers powerful inheritance features. However, not every class is designed to be extended. That’s where the final keyword comes in.

A final class explicitly tells PHP that this class cannot be inherited. It protects the class from being extended and helps preserve its intended behavior.

When you declare a class as final, PHP prevents any other class from extending it.

Trying to extend it results in a fatal error:

PHP 
class SampleGateway extends PaymentGateway
{
}

Fatal error: Class SampleGateway cannot extend final class PaymentGateway

PHP 
final class PaymentGateway
{
    public function process(): void
    {
         // ...
    }
}

# Why Use final?

Marking a class as final communicates an important design decision: This class is complete and should not be subclassed.

This has several benefits.

1.Protect Business Logic:

Some classes contain critical logic that should never be modified through inheritance. Using final guarantees that subclasses cannot override or change the behavior.

2.Make Your API Clear:

Developers immediately understand that inheritance is not part of the public API. Instead of extending the class, they should use composition or interfaces.

3.Prevent Fragile Inheritance:

Inheritance creates tight coupling. A parent class may unintentionally break child classes after internal changes. Making a class final eliminates this risk because no subclasses can exist.

# When Should You Use final

There isn’t a universal rule, but these are common scenarios.

  • Value Objects
  • Service Classes
  • Domain Objects with Fixed Behavior
  • Internal Library Classes

# When Should You Avoid final?

Avoid marking a class as final if you expect developers to extend it.

  • Framework base classes
  • Abstract classes
  • Extension points in packages
  • Classes specifically designed for inheritance

If inheritance is part of the design, final only makes the API less useful.

# Can use final for methods too

PHP allows final on both classes and individual methods.

PHP 
class Animal
{
      final public function sleep(): void
       {
       }
}

Here:

  • The class can be extended.
  • The sleep() method cannot be overridden.

When the entire class is marked final, none of its methods can be overridden because the class itself cannot be inherited.