PHP Final Class

final class ClassName {
    // Properties and methods
}

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Engine Behavior and Inheritance

final class ParentClass {
    public function execute(): void {}
}

// Fatal error: Class ChildClass may not inherit from final class (ParentClass)
class ChildClass extends ParentClass {
}

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Method Redundancy

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Instantiation and Composition

• It can be instantiated using the new keyword.
• It can inherit from another (non-final) class.
• It can implement one or more interfaces.
• It can import traits.

class BaseEntity {}
interface CustomSerializable {}
trait Timestampable {}

// Valid: A final class extending a base class, implementing an interface, and using a trait
final class User extends BaseEntity implements CustomSerializable {
    use Timestampable;
    
    public string $username;
}

$user = new User(); // Valid instantiation

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Structural Restrictions

• Abstract Modifier: A class cannot be declared as both abstract and final simultaneously. These modifiers are mutually exclusive. Attempting to combine them (abstract final class) will result in a Fatal error: Cannot use the final modifier on an abstract class.
• Interfaces and Traits: The final keyword cannot be applied to interface or trait declarations. The PHP engine will throw a parse error, as the fundamental architecture of interfaces and traits requires them to be implemented or consumed by other structures.
• Readonly Classes: As of PHP 8.2, the final keyword can be combined with the readonly modifier (final readonly class Name {}).