class UrlValidator {
    private $url;

    function __construct($url){
        $this->checkUrl($url);
        $this->url = $url;
    }

    private function checkUrl($url){
        $urlHeaders = get_headers($url);
        if ($urlHeaders[0] == 'HTTP/1.1 404 Not Found') {
            throw new Exception("Url is incorrect.");
        }
        return true;
    }

    public function getUrl(){
        echo $this->url;
    }
}

$a = new UrlValidator('https://www.paperplane.io/404');
$a -> getUrl();