public static <V extends @Nullable Object> V getDone(Future<V> future) throws ExecutionException {
    /*
     * We throw IllegalStateException, since the call could succeed later. Perhaps we "should" throw
     * IllegalArgumentException, since the call could succeed with a different argument. Those
     * exceptions' docs suggest that either is acceptable. Google's Java Practices page recommends

  @Override
  public boolean isCancelled() {
    final Object localValue = value;
    return localValue instanceof Cancellation;
  }

  /**
   * {@inheritDoc}
   *
   * <p>If a cancellation attempt succeeds on a {@code Future} that had previously been {@linkplain
   * #setFuture set asynchronously}, then the cancellation will also be propagated to the delegate
   * {@code Future} that was supplied in the {@code setFuture} call.
   *

      return key.hashCode() ^ value.hashCode();
    }

    @Override
    public V setValue(V newValue) {
      V oldValue = put(key, newValue);
      value = newValue; // only if put succeeds
      return oldValue;
    }
  }

  final class EntryIterator extends HashIterator<Entry<K, V>> {

    @Override
    public Entry<K, V> next() {
      return nextEntry();
    }