web service中的步骤返回类型可以是void 吗

[WebService(Namespace = "http://tempuri.org/")][WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)][System.ComponentModel.ToolboxItem(false)]// 若要允许使用 ASP.NET AJAX 从脚本中调用此 Web 服务，请取消对下行的注释。// [System.Web.Script.Services.ScriptService]public class WebService1 : System.Web.Services.WebService{    [WebMethod]    public string HelloWorld(ref string hi)    {        hi = " I'm " + hi;        return "Hello World. " + hi;    }    [WebMethod]    public void HelloWorldVoidRef(ref string hi)    {        hi = "Void I'm " + hi;    }    [WebMethod]    public void HelloWorldVoid()    {        // do something    }}