Shuffle a list of integers with Java 8 Streams API

Question

I tried to translate the following line of Scala to Java 8 using the Streams API:

// Scala
util.Random.shuffle((1 to 24).toList)

To write t

Answer 1

To perform a shuffle efficiently you need all the values in advance. You can use Collections.shuffle() after you have converted the stream to a list like you do in Scala.

Answer 2

If you're looking for a "streaming only" solution and a deterministic, merely "haphazard" ordering versus a "random" ordering is Good Enough, you can always sort your ints by a hash value:

List<Integer> xs=IntStream.range(0, 10)
    .boxed()
    .sorted( (a, b) -> a.hashCode() - b.hashCode() )
    .collect(Collectors.toList());

If you'd rather have an int[] than a List<Integer>, you can just unbox them afterwards. Unfortunately, you have go through the boxing step to apply a custom Comparator, so there's no eliminating that part of the process.

List<Integer> ys=IntStream.range(0, 10)
    .boxed()
    .sorted( (a, b) -> a.hashCode() - b.hashCode() )
    .mapToInt( a -> a.intValue())
    .toArray();