code: private static synchronized String getDefaultPattern() {
          ULocale defaultLocale = ULocale.getDefault(Category.FORMAT);
          if (!defaultLocale.equals(cachedDefaultLocale)) {
              cachedDefaultLocale = defaultLocale;
              Calendar cal = Calendar.getInstance(cachedDefaultLocale);
  
              try {
                  // Load the calendar data directly.
                  ICUResourceBundle rb = (ICUResourceBundle) UResourceBundle.getBundleInstance(
                          ICUData.ICU_BASE_NAME, cachedDefaultLocale);
                  String resourcePath = "calendar/" + cal.getType() + "/DateTimePatterns";
                  ICUResourceBundle patternsRb= rb.findWithFallback(resourcePath);
  
                  if (patternsRb == null) {
                      patternsRb = rb.findWithFallback("calendar/gregorian/DateTimePatterns");
                  }
                  if (patternsRb == null || patternsRb.getSize() < 9) {
                      cachedDefaultPattern = FALLBACKPATTERN;
                  } else {
                      int defaultIndex = 8;
                      if (patternsRb.getSize() >= 13) {
                          defaultIndex += (SHORT + 1);
                      }
                      String basePattern = patternsRb.getString(defaultIndex);
  
                      cachedDefaultPattern = SimpleFormatterImpl.formatRawPattern(
                              basePattern, 2, 2,
                              patternsRb.getString(SHORT), patternsRb.getString(SHORT + 4));
                  }
              } catch (MissingResourceException e) {
                  cachedDefaultPattern = FALLBACKPATTERN;
              }
          }
          return cachedDefaultPattern;
      }
docs: /*
  Returns the default date and time pattern (SHORT) for the default locale.
  This method is only used by the default SimpleDateFormat constructor.