code: public static String secs(int sec) {
          int hh = sec / 3600;
          sec -= hh * 3600;
          int mm = sec / 60;
          sec -= mm * 60;
          return Strings.alignRight(hh, 2, '0')
                 + ":"
                 + Strings.alignRight(mm, 2, '0')
                 + ":"
                 + Strings.alignRight(sec, 2, '0');
  
      }
docs: 根据一个当天的绝对秒数，得到一个时间字符串，格式为 "HH:mm:ss"
  
  @param sec
  当天的绝对秒数
  @return 时间字符串