public K getElement() {
      return key;
    }

    void updateLastKnownIndex() {
      if (lastKnownIndex == -1
          || lastKnownIndex >= size()
          || !Objects.equals(key, keys[lastKnownIndex])) {
        lastKnownIndex = indexOf(key);
      }
    }

    @Override
    public int getCount() {
      updateLastKnownIndex();
      return (lastKnownIndex == -1) ? 0 : values[lastKnownIndex];
    }

      this.key = key(index);
      this.lastKnownIndex = index;
    }

    @Override
    @ParametricNullness
    public K getKey() {
      return key;
    }

    private void updateLastKnownIndex() {
      if (lastKnownIndex == -1
          || lastKnownIndex >= size()
          || !Objects.equals(key, key(lastKnownIndex))) {
        lastKnownIndex = indexOf(key);
      }
    }

    @Override

      this.key = key(index);
      this.lastKnownIndex = index;
    }

    @Override
    @ParametricNullness
    public K getKey() {
      return key;
    }

    private void updateLastKnownIndex() {
      if (lastKnownIndex == -1
          || lastKnownIndex >= size()
          || !Objects.equals(key, key(lastKnownIndex))) {
        lastKnownIndex = indexOf(key);
      }
    }

    @Override