On 12 Mar 2015, at 09:44, Paul Sandoz <paul.san...@oracle.com> wrote:
> > On Mar 11, 2015, at 1:45 PM, Aggelos Biboudis <bibou...@gmail.com> wrote: > >> Hi all, >> >> Please review the patch for the count terminal operator on SIZED streams. >> >> https://bugs.openjdk.java.net/browse/JDK-8067969 >> http://cr.openjdk.java.net/~psandoz/jdk9/JDK-8067969-optimize-stream-count/webrev/ >> >> Thanks Paul Sandoz for sponsoring this. >> > > This looks good. Code is nicely contained and not as much as i initially > anticipated. This does indeed look nice. One, trivial, question why call spliterator.getExactSizeIfKnown() and not spliterator.estimateSize() ? > I am pondering adding an api note to the count methods to head off any > suprises as now the stream pipeline may not be executed. I think it would be good to add a note to the spec, as this could be surprising. So really this comes down to the type if intermediate operations, right? For example, filter will always be executed: IntStream.of(1, 2, 3, 4).peek(System.out::println).filter(x -> true).count(); Should the note capture something about the type of the intermediate operations? > * @apiNote > * An implementation may choose to not execute the stream pipeline (either > * sequentially or in parallel) if it is capable of computing the count > * directly from the stream source. In such cases no source elements will > * be traversed and no intermediate operations will be evaluated. > * Behavioral parameters with side-effects, which are strongly discouraged > * except for harmless cases such as debugging, may be affected. For > * example, consider the following stream: > * <pre>{@code > * List<String> l = ... > * long count = l.stream().peek(System.out::println).count(); > * }</pre> > * The number of elements covered by the stream source, a {@code List}, is > * known and the intermediate operation, {@code peek}, does not inject into > * or remove elements from the stream. Thus the count is the size of the > * {@code List} and there is no need to execute the pipeline and, as a > * side-effect, print out the list elements. > > WDYT? > > Paul. -Chris.
