cdm/src/main/java/ucar/nc2/time/CalendarPeriod.java
public static CalendarPeriod of(int value, Field field) {
    CalendarPeriod want = new CalendarPeriod(value, field);
    if (cache == null) return want;
    CalendarPeriod got = cache.getIfPresent(want);
    if (got != null) return got;
    cache.put(want, want);
    return want;
  }
public static CalendarPeriod of(int value, Field field) {
    CalendarPeriod want = new CalendarPeriod(value, field);
    if (cache == null) return want;
    CalendarPeriod got = cache.getIfPresent(want);
    if (got != null) return got;
    cache.put(want, want);
    return want;
  }
minimize memory use by interning. wacko shit in GribPartitionBuilder TimeCoordinate, whoduhthunk?