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

Creates a lazily concatenated stream whose elements are all the elements of the first stream followed by all the elements of the second stream. The resulting stream is ordered if both of the input streams are ordered, and parallel if either of the input streams is parallel. When the resulting stream is closed, the close handlers for both input streams are invoked.

This method operates on the two input streams and binds each stream to its source. As a result subsequent modifications to an input stream source may not be reflected in the concatenated stream result.

Parameters:

<T>		The type of stream elements
a		the first stream
b		the second stream

Returns:  the concatenation of the two input streams

@implNote Use caution when constructing streams from repeated concatenation. Accessing an element of a deeply concatenated stream can result in deep call chains, or even StackOverflowError.

Subsequent changes to the sequential/parallel execution mode of the returned stream are not guaranteed to be propagated to the input streams.
@apiNote To preserve optimization opportunities this method binds each stream to its source and accepts only two streams as parameters. For example, the exact size of the concatenated stream source can be computed if the exact size of each input stream source is known. To concatenate more streams without binding, or without nested calls to this method, try creating a stream of streams and flat-mapping with the identity function, for example:

     Stream<T> concat = Stream.of(s1, s2, s3, s4).flatMap(s -> s);