code: static UnitPatterns of(Locale lang) {
  
          if (lang == null) {
              throw new NullPointerException("Missing language.");
          }
  
          UnitPatterns p = CACHE.get(lang);
  
          if (p == null) {
              p = new UnitPatterns(lang);
              UnitPatterns old = CACHE.putIfAbsent(lang, p);
              if (old != null) {
                  p = old;
              }
          }
  
          return p;
  
      }
docs: <p>Factory method as constructor replacement. </p>
  
  @param   lang    language setting
  @return  chached instance