code: protected Calendar guessCalendar() {
          ULocale calLocale = getAvailableLocale(TYPE_CALENDAR);
          if (calLocale == null) {
              calLocale = ULocale.US;
          }
          return Calendar.getInstance(getTimeZone(), calLocale);
      }
docs: This function can be overridden by subclasses to use different heuristics.
  <b>It MUST return a 'safe' value,
  one whose modification will not affect this object.</b>
  
  @hide draft / provisional / internal are hidden on Android