NOTE: nosid’s answer shows how to add to an existing collection using forEachOrdered(). This is a useful and effective technique for mutating existing collections. My answer addresses why you shouldn’t use a Collector to mutate an existing collection. The short answer is no, at least, not in general, you shouldn’t use a Collector to modify … Read more
There are functions in the Kotlin stdlib for average, count, distinct,filtering, finding, grouping, joining, mapping, min, max, partitioning, slicing, sorting, summing, to/from arrays, to/from lists, to/from maps, union, co-iteration, all the functional paradigms, and more. So you can use those to create little 1-liners and there is no need to use the more complicated syntax … Read more
There are new methods added to java.util.Arrays to convert an array into a Java 8 stream which can then be used for summing etc. int sum = Arrays.stream(myIntArray).sum(); Multiplying two arrays is a little more difficult because I can’t think of a way to get the value AND the index at the same time as … Read more
For the specific question of generating a reverse IntStream, try something like this: static IntStream revRange(int from, int to) { return IntStream.range(from, to) .map(i -> to – i + from – 1); } This avoids boxing and sorting. For the general question of how to reverse a stream of any type, I don’t know of … Read more
Operations takeWhile and dropWhile have been added to JDK 9. Your example code IntStream .iterate(1, n -> n + 1) .takeWhile(n -> n < 10) .forEach(System.out::println); will behave exactly as you expect it to when compiled and run under JDK 9. JDK 9 has been released. It is available for download here: JDK 9 Releases.
Original answer Yes, this is possible: List<BigDecimal> bdList = new ArrayList<>(); //populate list BigDecimal result = bdList.stream() .reduce(BigDecimal.ZERO, BigDecimal::add); What it does is: Obtain a List<BigDecimal>. Turn it into a Stream<BigDecimal> Call the reduce method. 3.1. We supply an identity value for addition, namely BigDecimal.ZERO. 3.2. We specify the BinaryOperator<BigDecimal>, which adds two BigDecimal‘s, via … Read more
UPDATE: This answer is in response to the original question, Does Java SE 8 have Pairs or Tuples? (And implicitly, if not, why not?) The OP has updated the question with a more complete example, but it seems like it can be solved without using any kind of Pair structure. [Note from OP: here is … Read more
Let me explain what is happening here, because it isn’t obvious! First, Stream.max() accepts an instance of Comparator so that items in the stream can be compared against each other to find the minimum or maximum, in some optimal order that you don’t need to worry too much about. So the question is, of course, … Read more
You need to wrap your method call into another one, where you do not throw checked exceptions. You can still throw anything that is a subclass of RuntimeException. A normal wrapping idiom is something like: private void safeFoo(final A a) { try { a.foo(); } catch (Exception ex) { throw new RuntimeException(ex); } } (Supertype … Read more
Don’t worry about any performance differences, they’re going to be minimal in this case normally. Method 2 is preferable because it doesn’t require mutating a collection that exists outside the lambda expression. it’s more readable because the different steps that are performed in the collection pipeline are written sequentially: first a filter operation, then a … Read more