code: @Override
      public final boolean containsKey(Object key) {
          long hash;
          return segment(segmentIndex(hash = keyHashCode(key))).find(this, hash, key) > 0;
      }
docs: Returns {@code true} if this map contains a mapping for the specified key. More formally,
  returns {@code true} if and only if this map contains a mapping for a key {@code k} such that
  {@link #keysEqual(Object, Object) keysEqual(key, k)}{@code == true}. (There can be at most
  one such mapping.)
  
  @param key key whose presence in this map is to be tested
  @return {@code true} if this map contains a mapping for the specified key