code: public V putIfNew(K key, V value)
    {
      V oldValue = compareAndPut(null, key, value, true);
  
      if (oldValue != null)
        return oldValue;
      else
        return value;
    }
docs: Puts a new item in the cache.  If the cache is full, remove the
  LRU item.
  
  @param key key to store data
  @param value value to be stored
  
  @return the value actually stored