Appending data to an anchor tag

PHP Snippet 1:

<a href="?ref=login_detail&id=<?php echo $car_id ?>">Hello</a>

PHP Snippet 2:

var_dump($_GET['id']);

PHP Snippet 3:

class Obj
{
    public function login_detail($id)
    {
        //do something with passed $id
        echo $id;
    }
}

(...)
$obj = new Obj();
$obj->login_detail($_GET['id']);

PHP Snippet 4:

class Obj
{
    public function login_detail($id)
    {
        echo $_GET['id'];
    }
}
$obj = new Obj();
$obj->login_detail();