public static <K, V> ImmutableSet<K> allKeys(final Iterable<? extends Map<K, V>> maps) {
    final ImmutableSet.Builder<K> builder = ImmutableSet.builder();

    for (final Map<K, V> map : maps) {
      builder.addAll(map.keySet());
    }

    return builder.build();
  }
public static < K , V > ImmutableSet < K > allKeys ( final Iterable < ? extends Map < K , V > > maps ) { final ImmutableSet . Builder < K > builder = ImmutableSet . builder ( ) ; for ( final Map < K , V > map : maps ) { builder . addAll ( map . keySet ( ) ) ; } return builder . build ( ) ; }
Gets the union of the {@code keySet()}s of all provided {@link Maps}s.