Java 8 threads adding values ​​from two or more lists

Question

I am trying to get into Java 8 and get my head around threads and lambda to solve various problems and am stuck on this particular one, which I usually use forEach and store values ​​in Map for solution.

How could you write code to get the expected list using new features in Java 8?

List<Integer> voterA = Arrays.asList(1,2,3,4,5); List<Integer> voterB = Arrays.asList(1,2,3,4,5); List<List<Integer>> votes = Arrays.asList(voterA, voterB); // expected list = (2,4,6,8,10) List<Integer> sumVotes = ... 

Answer 1

In fact, this is not how you hope. The closest thing you could probably get would be

 IntStream.range(0, voterA.size()) .mapToObj(i -> voterA.get(i) + voterB.get(i)) .collect(toList()); 

... but there is no "zip" operation in the streams, mainly because two different streams may have backup delimiters that break up at different points, so you cannot align them correctly.

Answer 2

JDK does not provide a zip API. But this can be done using the third AbacusUtil library:

 List<Integer> voterA = Arrays.asList(1, 2, 3, 4, 5); List<Integer> voterB = Arrays.asList(1, 2, 3, 4, 5); List<Integer> sumVotes = Stream.zip(voterA, voterB, (a, b) -> a + b).toList(); 

Disclosure: I am a developer of AbacusUtil.