code: private void initialize(Locale loc) {
          // Verify and compile the given pattern.
          compiledPattern = compile(pattern);
  
          /* try the cache first */
          numberFormat = cachedNumberFormatData.get(loc);
          if (numberFormat == null) { /* cache miss */
              numberFormat = NumberFormat.getIntegerInstance(loc);
              numberFormat.setGroupingUsed(false);
  
              /* update cache */
              cachedNumberFormatData.putIfAbsent(loc, numberFormat);
          }
          numberFormat = (NumberFormat) numberFormat.clone();
  
          initializeDefaultCentury();
      }
docs: /* Initialize compiledPattern and numberFormat fields