请问如下代码中$oa = Single::getinstance();这句就相当于实例化吗？为什么可以直接使用Single::getinstance();就可以访问这个类中的方法？谢谢

class Single{

    private $name;
    private function __construct(){

    }

    static public $instance;

    static public function getinstance(){
        if(!self::$instance) self::$instance = new self();
        return self::$instance;
    }

    public function setname($n){
        $this->name = $n;
    }

    public function getname(){
        return $this->name;
    }
}

    $oa = Single::getinstance();
    $ob = Single::getinstance();

    $oa->setname('hello world');
    $ob->setname('good morning');

    echo $oa->getname();
    echo '<br/>';
    echo $ob->getname();