A little question about singleton mode

Recently, I started some small projects and came into contact with the simple profit model. Based on the principle of hiding information as much as possible when defining classes, I wrote the following classes

<code>class openGate{
        private $dbname='mysql:host=localhost;dbname=project';
        private    $username='root';
        private    $password='root';
        private static $key=null;
        private function __construct(){}
        private function __clone(){}
        public static function gateKey(){
            if (self::$key==null) {
                self::$key=new openGate();
                return self::$key->gateWay();
            }
            return self::$key->gateway();
        }
        public function gateWay(){
            return new PDO($this->dbname,$this->username,$this->password);
        }
    }
    $person=openGate::gateKey();
    var_dump($person);</code>

Excuse me, how does this compare with the following

<code>class openGate{
        private static $key=null;
        private function __construct(){}
        private function __clone(){}
        public static function gateKey(){
            if (self::$key==null) {
                $dbname='mysql:host=localhost;dbname=project';
                $username='root';
                $password='root';
                return self::$key=new PDO($dbname,$username,$password);
            }
            return self::$key;
        }
    }
    $person=openGate::gateKey();
    var_dump($person);</code>

What are the pros and cons, or is it just redundant?