886 

   887     /**

   888      * Creates a lazy concatenated {@code Stream} whose elements are all the

   889      * elements of a first {@code Stream} succeeded by all the elements of the

   890      * second {@code Stream}. The resulting stream is ordered if both

   891      * of the input streams are ordered, and parallel if either of the input

   892      * streams is parallel.

   893      *

   894      * @param <T> The type of stream elements

   895      * @param a the first stream

   896      * @param b the second stream to concatenate on to end of the first

   897      *        stream

   898      * @return the concatenation of the two input streams

   899      */

   900     public static <T> Stream<T> concat(Stream<? extends T> a, Stream<? extends T> b) {

   901         Objects.requireNonNull(a);

   902         Objects.requireNonNull(b);

   903 

   904         @SuppressWarnings("unchecked")

   905         Spliterator<T> split = new Streams.ConcatSpliterator.OfRef<>(

   906                 (Spliterator<T>) a.spliterator(), (Spliterator<T>) b.spliterator());

   907         return (a.isParallel() || b.isParallel())

   908                ? StreamSupport.parallelStream(split)

   909                : StreamSupport.stream(split);

   910     }