this.previousWrite = previous;
    }
  }

  /** Used for weakly-referenced keys. */
  static class WeakEntry<K, V> extends WeakReference<K> implements ReferenceEntry<K, V> {
    WeakEntry(ReferenceQueue<K> queue, K key, int hash, @CheckForNull ReferenceEntry<K, V> next) {
      super(key, queue);
      this.hash = hash;
      this.next = next;
    }