Substream applied to unordered streams
paul.sandoz at oracle.com
Sun Mar 17 12:30:32 PDT 2013
On Mar 16, 2013, at 9:43 PM, Georgiy Rakov <georgiy.rakov at oracle.com> wrote:
> In general I asked whether you see useful to show these points in spec,
> e. g. if spec contains something like:
> You should keep in mind that substream() could return stream which
> content is nondeterministic provided original stream encounter order
> is not defined, e.g. for stream returned from HashSet instance.
It cuts deeper than that.
If a source does not have encounter order then by definition traversal of that source, using say an Iterator or a Spliterator, may be non-determinisitic.
This can even apply to the splitting of a Spliterator. If such a Spliterator does not have an encounter order, then when split it is free to partition in anyway appropriate to its internal data structures, for example try this:
Map<Integer, Integer> m = new ConcurrentHashMap<>();
for (int i = 0; i < 10000; i++) m.put(i, i);
List<Integer> lRoot = new ArrayList<>();
List<Integer> lLeftRight = new ArrayList<>();
Spliterator<Integer> right = m.keySet().spliterator();
Spliterator<Integer> left = right.trySplit();
System.out.println(lLeftRight.size() == lRoot.size());
System.out.println(new HashSet(lRoot).equals(new HashSet(lLeftRight)));
It should print out:
More information about the lambda-dev