collectors

I want to use Java 8 streams to convert a List of String values to a single String. A List of values like "A", "B" should return a String like "Values: 'A', 'B' added". This works fine, however I want to change the Pre- and Postfix depending on the amount of values. For example, if I have a List of only "A" I want the resulting String to be "Value 'A' added". import java.util.stream.Collectors; import java.util.ArrayList; import java.util.List; public class HelloWorld { public static void main(String[] args) { List<String> values = new ArrayList<>(); values.add("A"); values.add("B"); values

(This is probably related to https://stackoverflow.com/a/30312177/160137 , but I'm afraid I still don't get it. So I'm asking my question this way, in the hope that it'll lead to an answer I can more easily understand.) Normally when I have a Stream I can convert it to a collection using one of the static methods in the Collectors class: List<String> strings = Stream.of("this", "is", "a", "list", "of", "strings") .collect(Collectors.toList()); The similar process doesn't work on primitive streams, however, as others have noticed: IntStream.of(3, 1, 4, 1, 5, 9) .collect(Collectors.toList()); //

As for example, there are two lists: List<Double> list1 = Arrays.asList(1.0, 2.0); List<String> list2 = Arrays.asList("one_point_zero", "two_point_zero"); Using Stream, I want to create a map composed of these lists, where list1 is for keys and list2 is for values. To do it, I need to create an auxiliary list: List<Integer> list0 = Arrays.asList(0, 1); Here is the map: Map<Double, String> map2 = list0.stream() .collect(Collectors.toMap(list1::get, list2::get)); list0 is used in order list1::get and list2::get to work. Is there a simpler way without creation of list0? I tried the following code

I have Map<A, Map<B, C>> and I want to get Map<B, List<C>> from it using Java Streams. I try to do it as follows: public <A, B, C> Map<B, List<C>> groupsByInnerKey(Map<A, Map<B, C>> input) { return input.values() .stream() .flatMap(it -> it.entrySet().stream()) .collect(Collectors.groupingBy(Map.Entry::getKey)); } What I expect: flatMap gives a Stream of Map.Entry<B, C> collect(Collectors.groupingBy(...)) takes function which is applied to Map.Entry<B, C> and returns B , thus it collects values of C into List<C> . But it doesn't compile, literally: Non-static method cannot be referenced from a

This is a continuation of my previous question at Group, Sum byType then get diff using Java streams . As suggested, I should post as a separate thread instead of updating the original one. So with my previous set of question, I have achieved that, and now, with the continuation. Background: I have the following dataset Sample(SampleId=1, SampleTypeId=1, SampleQuantity=5, SampleType=ADD), Sample(SampleId=2, SampleTypeId=1, SampleQuantity=15, SampleType=ADD), Sample(SampleId=3, SampleTypeId=1, SampleQuantity=25, SampleType=ADD), Sample(SampleId=4, SampleTypeId=1, SampleQuantity=5, SampleType