Convert Map<Integer, List<Integer>> to List<Integer> using java8 streams

Question

I liked Streams concept in java 8 . Now I want to convert a Map in java to a sorted List with the help of Java Streams. I just want to display the list without storing it anywhere. I want this output in resulting list:

5, 7, 8, 10, 19, 20, 22, 28, 30, 35, 40, 45, 50 .

Here's my code:

    Map<Integer, List<Integer>> obj=new HashMap<Integer, List<Integer>>();
    obj.put(5, Arrays.asList(7,8,30));
    obj.put(10, Arrays.asList(20));
    obj.put(19, Arrays.asList(22,50));
    obj.put(28, Arrays.asList(35,40,45));

Eran · Accepted Answer · 2017-04-20 08:26:07Z

10

I don't see why anyone would want to do that (except for playing with Streams), but you can convert the Map to a flat Stream of Integers and then sort it:

List<Integer> sorted =
    obj.entrySet()
       .stream()
       .flatMap(e-> Stream.concat(Stream.of(e.getKey()),e.getValue().stream()))
       .sorted()
       .collect(Collectors.toList());

answered Apr 20, 2017 at 8:26

Eran

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1 Comment

raj Over a year ago

I just wanted to find another way to flatten a linked list . geeksforgeeks.org/flattening-a-linked-list

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