code: public DbxLongpollDeltaResult getLongpollDelta(String cursor, int timeout)
          throws DbxException
      {
          if (cursor == null) throw new IllegalArgumentException("'cursor' can't be null");
          if (timeout < 30 || timeout > 480) throw new IllegalArgumentException("'timeout' must be >=30 and <= 480");
          String[] params = {
                  "cursor", cursor,
                  "timeout", Integer.toString(timeout),
          };
  
          return DbxRequestUtil.doGet(
              getRequestConfig(),
              getAccessToken(),
              USER_AGENT_ID,
              host.getNotify(),
              "1/longpoll_delta",
              params,
              null,
              new DbxRequestUtil.ResponseHandler<DbxLongpollDeltaResult>() {
                  @Override
                  public DbxLongpollDeltaResult handle(HttpRequestor.Response response)
                      throws DbxException
                  {
                      if (response.getStatusCode() != 200) throw DbxRequestUtil.unexpectedStatus(response);
                      return DbxRequestUtil.readJsonFromResponse(DbxLongpollDeltaResult.Reader, response);
                  }
              }
          );
      }
docs: Waits for changes to files on an account, starting from the state represented by {@code cursor}.
  
  @param cursor
  A cursor returned by ono of the "delta" methods.
  
  @param timeout
  How long poll should run before timing out, in seconds.