code: protected boolean use12HourFormat()
      {
          final String pattern = DateTimeFormat.patternForStyle("-S", getLocale());
          return pattern.indexOf('a') != -1 || pattern.indexOf('h') != -1 || pattern.indexOf('K') != -1;
      }
docs: Depending on the locale am/pm is used or not.
  
  @return true if 12 hour format else false