java-stream

Premise : I've already read this question and others, but I need some clarifications. I understand that Stream.forEach method makes the difference (not only) when dealing with parallel streams, and this explains why this //1 Stream.of("one ","two ","three ","four ","five ","six ") .parallel() .forEachOrdered(item -> System.out.print(item)); prints one two three four five six But when it comes to intermediate operations, the order is not guaranteed anymore when stream is parallelized. So this code //2 Stream.of("one ","two ","three ","four ","five ","six ") .parallel() .peek(item -> System.out

I'm having a problem with the Map<Integer, List<String>> personenPerLeeftijd , the compiler says the method, Persoon::getLeeftijd, cannot be resolved. I don't really know what else I can do, sorry for the Dutch words! I you need any more info pls ask so public class TestPersoon2 { public static void main(String[] args) { final List<Persoon> personen = Personen.getPersonen(); Map<String, Persoon> map = personen.stream().collect(Collectors.toMap(p -> p.getNaam() + "-" + p.getLeeftijd(), p -> p)); for (String s : map.keySet()) { System.out.printf("%-15s -> %s\n", s, map.get(s)); } Map<Integer,

I am trying to do a map operation on a List<Integer> : list.stream().map(i -> i - 2).collect(Collectors.toList()); Instead of performing the operation on the last element of the list, I would like it to just be passed through. ...Collectors.toList()).add(i) doesn't work, of course, because i is out of scope. For example, the input list [1, 2, 3, 4] should output [-1, 0, 1, 4] You could stream the original list and limit the stream to exclude the last element, do the mapping and collect to a new ArrayList , then add the last element of the original list to the last position of the new, mutable

Sample code: class Outer { public Integer i; Outer(Integer i) { this.i = i; } public int getVal() { return i; } } class MyClass { public Integer f(Outer o) { return o.getVal();}; public void main() { MyClass g = new MyClass(); List<Integer> l1 = Arrays.asList(new Outer(2)).stream().map(g::f).collect(Collectors.toList()); List<Integer> l2 = Arrays.asList(new Outer(2)).stream().map(Outer::getVal).collect(Collectors.toList()); } } Using either of the method references of Outer::instanceMethod that takes no argument and is basically a Supplier<T> functional interface. [1] MyClass::instanceMethod

There are some SQL statements in my program that contain IN -clauses with given Ids. The problem is that in some cases there might be more than 1000 Ids which causes Oracle to crash with ORA-01795. Too many items. So I want to divide this list into multiple sub-lists. Example: I have 2403 Ids Result would be three lists: 0 - 999 1000 - 1999 2000 - 2402 I have written a piece of code that works, but looks terrible. Is there any better solution for this problem? Maybe something with Collectors & groupingby or anything like that? My code: Map<Integer, List<Long>> result = new HashMap<>();