Will the Singleton pattern work if it has already been initialized earlier?

The Singleton pattern guarantees that a class has only one instance and provides a global point of access to it. If the Singleton has already been initialized earlier, subsequent calls to get the instance will return this already created object, rather than creating a new one.

Thus, the Singleton pattern will continue to work correctly, ensuring the uniqueness of the instance throughout the application's lifetime.

Example in PHP:

class Singleton {
    private static $instance = null;

    private function __construct() {
        // private constructor
    }

    public static function getInstance() {
        if (self::$instance === null) {
            self::$instance = new Singleton();
        }
        return self::$instance;
    }
}

$first = Singleton::getInstance();
$second = Singleton::getInstance();
var_dump($first === $second); // bool(true)