}

    @Override
    public void notifyNewValue(V newValue) {}
  }

  /** References a weak value. */
  private static final class WeightedWeakValueReference<K, V> extends WeakValueReference<K, V> {
    final int weight;

    WeightedWeakValueReference(
        ReferenceQueue<V> queue, V referent, ReferenceEntry<K, V> entry, int weight) {
      super(queue, referent, entry);
      this.weight = weight;