code: static ObjectIdentifier intern(ObjectIdentifier oid) {
          ObjectIdentifier interned = internedOIDs.get(oid);
          if (interned != null) {
              return interned;
          }
          internedOIDs.put(oid, oid);
          return oid;
      }
docs: /*
  Maybe return a preallocated OID, to reduce storage costs
  and speed recognition of common X.500 attributes.