java-stream

I actually tried to answer this question How to skip even lines of a Stream<String> obtained from the Files.lines . So I though this collector wouldn't work well in parallel: private static Collector<String, ?, List<String>> oddLines() { int[] counter = {1}; return Collector.of(ArrayList::new, (l, line) -> { if (counter[0] % 2 == 1) l.add(line); counter[0]++; }, (l1, l2) -> { l1.addAll(l2); return l1; }); } but it works. EDIT: It didn't actually work; I got fooled by the fact that my input set was too small to trigger any parallelism; see discussion in comments . I thought it wouldn't work

I am building an object with a simple loop: WebTarget target = getClient().target(u); for (Entry<String, String> queryParam : queryParams.entrySet()) { target = target.queryParam(queryParam.getKey(), queryParam.getValue()); } I want to do the same thing using the Java8 Stream API but I cannot figure out how to do it. What makes me struggle is that target is reassigned every time, so a simple .forEach() will not work. I guess I need to use a .collect() or reduce() since I am looking for a single return value but I am lost at the moment! aioobe There's unfortunately no foldLeft method in the

I have a List like this: List<Map<String, Long>> Is there a way, using lambda, to convert this list to: Map<String, List<Long>> Example: Map<String, Long> m1 = new HashMap<>(); m1.put("A", 1); m1.put("B", 100); Map<String, Long> m2 = new HashMap<>(); m2.put("A", 10); m2.put("B", 20); m2.put("C", 100); List<Map<String, Long>> beforeFormatting = new ArrayList<>(); beforeFormatting.add(m1); beforeFormatting.add(m2); After formatting: Map<String, List<Long>> afterFormatting; which would look like: A -> [1, 10] B -> [100, 20] C -> [100] You need to flatMap the entry set of each Map to create a

java.util.stream.Stream interface has two versions of sorted method – sorted() which sorts elements in natural order and sorted(Comparator) . Why min() method was not introduced to Stream interface, which would return minimal element from natural-ordering point of view? Holger It should be clear that for min , max , and sorted , adding a method to Stream that does not require a comparator introduces a way to lose the generic type safety. The reason is that the current version of the Java language does not support restricting methods to instances of a specific parameterization, i.e. limit them

I was reading about statelessness and came across this in doc : Stream pipeline results may be nondeterministic or incorrect if the behavioral parameters to the stream operations are stateful. A stateful lambda (or other object implementing the appropriate functional interface) is one whose result depends on any state which might change during the execution of the stream pipeline. Now if I have the a list of string ( strList say) and then trying to remove duplicate strings from it using parallel streams in the following way: List<String> resultOne = strList.parallelStream().distinct().collect

I am trying to convert the following text input file: A=groupA1 A=groupA2 A=groupA3 B=groupB1 B=groupB2 into Map<String, List<String>> by splitting each line on "=" So far I manged to get this sort of output: KEY: A VALUE: A=groupA1 VALUE: A=groupA2 VALUE: A=groupA3 KEY: B VALUE: B=groupB1 VALUE: B=groupB2 using such code: File reqFile = new File("test.config"); try (Stream<String> stream = Files.lines(reqFile.toPath())) { Map<String, List<String>> conf = stream.collect(Collectors.groupingBy(s -> s.split("=")[0])); for (Map.Entry<String, List<String>> entry: conf.entrySet()) { System.out

I have a method which generates an object each time I execute it, and I need to reverse the order with which I am getting them. So I thought the natural way to do it would be a Stack, since it is LIFO. However, the Java Stack does not seem to play well with the new Java 8 streaming API. If I do this: Stack<String> stack = new Stack<String>(); stack.push("A"); stack.push("B"); stack.push("C"); List<String> list = stack.stream().collect(Collectors.toList()); System.out.println("Collected: " + list); The output I get is: Collected: [A, B, C] Why isn't it outputing them in the expected LIFO order