code: public static JapaneseEra of(int japaneseEra) {
          JapaneseEra[] known = KNOWN_ERAS.get();
          if (japaneseEra < MEIJI.eraValue || japaneseEra > known[known.length - 1].eraValue) {
              throw new DateTimeException("japaneseEra is invalid");
          }
          return known[ordinal(japaneseEra)];
      }
docs: Obtains an instance of {@code JapaneseEra} from an {@code int} value.
  <p>
  The {@link #SHOWA} era that contains 1970-01-01 (ISO calendar system) has the value 1
  Later era is numbered 2 ({@link #HEISEI}). Earlier eras are numbered 0 ({@link #TAISHO}),
  -1 ({@link #MEIJI}), only Meiji and later eras are supported.
  
  @param japaneseEra  the era to represent
  @return the {@code JapaneseEra} singleton, not null
  @throws DateTimeException if the value is invalid