Method concat

guava/src/com/google/common/collect/Streams.java:185–209

Returns a {@link Stream} containing the elements of the first stream, followed by the elements of the second stream, and so on. <p>This is equivalent to {@code Stream.of(streams).flatMap(stream -> stream)}, but the returned stream may perform better. @see Stream#concat(Stream, Stream)

(Stream<? extends T>... streams)

   * @see Stream#concat(Stream, Stream)
   */
  @SuppressWarnings("unchecked") // could probably be avoided with a forwarding Spliterator
  @SafeVarargs
  public static <T extends @Nullable Object> Stream<T> concat(Stream<? extends T>... streams) {
    // TODO(lowasser): consider an implementation that can support SUBSIZED
    boolean isParallel = false;
    int characteristics = Spliterator.ORDERED | Spliterator.SIZED | Spliterator.NONNULL;
    long estimatedSize = 0L;
    ImmutableList.Builder<Spliterator<? extends T>> splitrsBuilder =
        new ImmutableList.Builder<>(streams.length);
    for (Stream<? extends T> stream : streams) {
      isParallel |= stream.isParallel();
      Spliterator<? extends T> splitr = stream.spliterator();
      splitrsBuilder.add(splitr);
      characteristics &= splitr.characteristics();
      estimatedSize = LongMath.saturatedAdd(estimatedSize, splitr.estimateSize());
    }
    return StreamSupport.stream(
            CollectSpliterators.flatMap(
                splitrsBuilder.build().spliterator(),
                splitr -> (Spliterator<T>) splitr,
                characteristics,
                estimatedSize),
            isParallel)
        .onClose(() -> closeAll(streams));
  }

  /**
   * Returns an {@link IntStream} containing the elements of the first stream, followed by the