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Re: .parallelStream()

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  Re: .parallelStream() Eric Sosman <esosman@comcast-dot-net.invalid> - 2015-04-01 10:19 -0400

#31434 — Re: .parallelStream()

On 4/1/2015 10:08 AM, Stefan Ram wrote:
>    I read somewhere that streams can be executed in parallel.
>
>    Somewhere else I read, that one needs to call
>    ».parallelStream()« for parallel execution.
>
>    So, do I get it right, that the JVM will never execute a
>    stream obtained by ».stream()« in parallel, even if it can
>    detect that this will be faster and yield the same outcome,
>    unless the programmer has explicitly enabled this via
>    ».parallelStream()«?

     Quoth the Javadoc for Collection (emphasis mine):

	default Stream<E> stream()
	Returns a *sequential* Stream with this collection as its
	source.

However, the sequential or parallel state of a Stream at the time
of creation need not be the final word; for some Streams it may be
possible to change the mode (before use, obviously).  The Javadoc
for BaseStream says (emphasis again mine):

	S parallel()

	Returns an equivalent stream that is parallel. May return
	itself, either because the stream was already parallel, or
	because the underlying stream state was *modified* to be
	parallel.

That is, it is possible that a Stream obtained from stream(), although
initially sequential, could become parallel later on.

-- 
esosman@comcast-dot-net.invalid
"Don't be afraid of work. Make work afraid of you." -- TLM

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