namespace UserAdmin;
class Adminuser {
    public $username;
    public $password;
}

namespace SectionAdminBundleController;
use UserAdmin;
class DefaultController extends Controller
{
    public function indexAction()
    {
        $AdminUser = new UserAdminAdminuser();  // CLASS NOT FOUND!!
        .......

namespace UserAdmin;

namespace UserAdmin;

"autoload": {
    "psr-0": { "": "src/" }
},

"autoload": {
    "psr-0": { "": "src/" },
    "psr-0": { "": "vendor/User/Admin" }
},