How to sort list in parallelStream?

Question

Is there a way to sort a list using parallelStream()? I saw there are forEach and forEachOrdered. But I was checking if there is a way to sort as follows,

list.parallelStream().map().sorted().collect(Collectors.toList());

Answer 1

A parallel stream is just a standard stream, so it is possible to apply sorted to a parallel stream. The result of the sorted method is a sequential stream.

So it works as follow:

 list.parallelStream()   // Generate a parallel stream
     .map(item -> ...)   // Item are mapped in parallel
     .sorted()           // sorted needs to wait for all elements before continuing
                         // Here the stream is sequential
     .collect(Collectors.toList());   // Collect to a new list

So sorted can operates on a parallel stream, but the resulting stream is sequential and it is released only after all elements of the parallel stream are received.

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Updated answer (thanks to @Louis Wasserman)

The result of sorted is not sequential. The terminal operation will maintain the same order of the original stream not depending on if it is a sequential stream or a parallel stream. So the correct code exposed before must be changed in the comments as below

 list.parallelStream()   // Generate a parallel stream
     .map(item -> ...)   // Item are mapped in parallel
     .sorted()           // sorted needs to wait for all elements before continuing
                         // REMOVED --> Here the stream is sequential
     .collect(Collectors.toList());   // Collect to a new list
                                      // ADDED --> in the same order of the received after the sorted step

If you add a map operation after the sorted with a random executing time you can see that this map operation can end in different moments, but at the end the collect will generate a List in the original order. (thanks to Louis Wasserman... I did a mistake I was not knowing the real internal details of stream, I hope that the updated answer give you the ability to better understand how streams works)