}
      };

  /** Concrete implementation of {@link WeakValueReference}. */
  static final class WeakValueReferenceImpl<K, V, E extends InternalEntry<K, V, E>>
      extends WeakReference<V> implements WeakValueReference<K, V, E> {
    @Weak final E entry;

    WeakValueReferenceImpl(ReferenceQueue<V> queue, V referent, E entry) {
      super(referent, queue);
      this.entry = entry;
    }