code: public void setID(String ID) {
          if (ID == null) {
              throw new NullPointerException();
          }
          if (isFrozen()) {
              throw new UnsupportedOperationException("Attempt to modify a frozen TimeZone instance.");
          }
          this.ID = ID;
      }
docs: Sets the time zone ID. This does not change any other data in
  the time zone object.
  @param ID the new time zone ID.