code: public Object lastKey() throws NoSuchElementException {
          Entry last = (mReverse) ? mMostRecent : mLeastRecent;
          if (last != null) {
              return last.mKey;
          }
          else if (mRecentMap.size() == 0) {
              throw new NoSuchElementException();
          }
          else {
              return null;
          }
      }
docs: Returns the last key in the map, the least recently used. If reverse
  order, then the most recently used is returned.