Class constants define values that cannot change and are associated with the class rather than instances. The final keyword prevents a class from being extended or a method from being overridden.
const NAME = value; inside a class defines a class constant.ClassName::CONSTANT or self::CONSTANT.final class prevents extension; final public function prevents override.<?php
class HttpStatus
{
// Class constants — typed since PHP 8.3
const int OK = 200;
const int CREATED = 201;
const int NO_CONTENT = 204;
const int BAD_REQUEST = 400;
const int UNAUTHORIZED = 401;
const int FORBIDDEN = 403;
const int NOT_FOUND = 404;
const int INTERNAL_SERVER_ERROR = 500;
private static array $messages = [
self::OK => 'OK',
self::CREATED => 'Created',
self::NOT_FOUND => 'Not Found',
self::INTERNAL_SERVER_ERROR => 'Internal Server Error',
];
public static function message(int $code): string
{
return self::$messages[$code] ?? 'Unknown';
}
}
echo HttpStatus::NOT_FOUND; // 404
echo HttpStatus::message(HttpStatus::OK); // OK
// final class — cannot be extended
final class Uuid
{
private function __construct(private readonly string $value) {}
public static function generate(): self
{
return new self(sprintf('%04x%04x-%04x-%04x-%04x-%04x%04x%04x',
mt_rand(0, 0xffff), mt_rand(0, 0xffff),
mt_rand(0, 0xffff),
mt_rand(0, 0x0fff) | 0x4000,
mt_rand(0, 0x3fff) | 0x8000,
mt_rand(0, 0xffff), mt_rand(0, 0xffff), mt_rand(0, 0xffff)
));
}
public function __toString(): string { return $this->value; }
}
$id = Uuid::generate();
echo $id; // e.g. a3f2b1c4-9d8e-4f7a-b2c1-0d3e4f5a6b7c
// class extends Uuid {} // Fatal error: Cannot extend final class
Tip: PHP 8.1 introduced enums, which are ideal for named constant sets like HTTP status codes or user roles. Consider using enum HttpStatus: int { case OK = 200; case NotFound = 404; } instead of class constants for these use-cases.