Hi, Please review this webrev that adds take/dropWhile operations to streams:
http://cr.openjdk.java.net/~psandoz/jdk9/JDK-8071597-take-drop-while/webrev/ I opted to weight the documentation of the operations towards ordered streams in the first paragraph. That is what makes most sense in terms of usage and what most people will read. Thus i refer to the "longest prefix" in the first paragraph then define what that means in subsequent paragraphs for ordered and unordered streams: 482 /** 483 * Returns a stream consisting of the longest prefix of elements taken from 484 * this stream that match the given predicate. 485 * 486 * <p>If this stream is ordered then the prefix is a contiguous sequence of 487 * elements of this stream. All elements of the sequence match the given 488 * predicate, the first element of the sequence is the first element 489 * (if any) of this stream, and the element (if any) immediately following 490 * the last element of the sequence does not match the given predicate. 491 * 492 * <p>If this stream is unordered then the prefix is a subset of elements of 493 * this stream. All elements (if any) of the subset match the given 494 * predicate. In this case the behavior of this operation is 495 * nondeterministic; it is free to select any valid subset as the prefix. 496 * 497 * <p>This is a <a href="package-summary.html#StreamOps">short-circuiting 498 * stateful intermediate operation</a>. 499 * ... 528 default Stream<T> takeWhile(Predicate<? super T> predicate) { 537 /** 538 * Returns a stream consisting of the remaining elements of this stream 539 * after dropping the longest prefix of elements that match the given 540 * predicate. 541 * 542 * <p>If this stream is ordered then the prefix is a contiguous sequence of 543 * elements of this stream. All elements of the sequence match the given 544 * predicate, the first element of the sequence is the first element 545 * (if any) of this stream, and the element (if any) immediately following 546 * the last element of the sequence does not match the given predicate. 547 * 548 * <p>If this stream is unordered then the prefix is a subset of elements of 549 * this stream. All elements (if any) of the subset match the given 550 * predicate. In this case the behavior of this operation is 551 * nondeterministic; it is free to select any valid subset as the prefix. 552 * ... 584 default Stream<T> dropWhile(Predicate<? super T> predicate) { After this has been reviewed i will follow up with a further issue regarding the specification of takeWhile, stateful predicates and cancellation. I avoided such specification here as it's likely to rathole :-) Basically the takeWhile operation is implemented such that one can do: long t = System.currentTimeMillis(); List<BigInteger> pps = Stream .generate(() -> BigInteger.probablePrime(1024, ThreadLocalRandom.current())) .parallel() .takeWhile(e -> (System.currentTimeMillis() - t) < TimeUnit.SECONDS.toMillis(5)) .collect(toList()); Paul.
