throw的一些用法

if (vp.ContainsKey("flag"))
            {
                int flagValue;
                int.TryParse(vp["flag"].ToString(), out flagValue);
                switch (flagValue)
                {
                    case 0:
                        linq = linq.Where(i => i.EndTime > DateTime.Now);
                        break;
                    case 1:
                        linq = linq.Where(i => i.EndTime <= DateTime.Now);
                        break;
                    case 2:
                       //...break;
                    default:
                        throw new ArgumentException("参数不正确");
                }
            }

public bool ValidateUser(string userName, string password)
        {
            if (String.IsNullOrEmpty(userName)) throw new ArgumentException("值不能为 null 或为空。", "userName");
            if (String.IsNullOrEmpty(password)) throw new ArgumentException("值不能为 null 或为空。", "password");

            return _provider.ValidateUser(userName, password);
        }