Java 8 stream returns list from element [duplicate]

Question

There is a simply:

public class Task{
   private String name;
   private List<Task> subtasks;
}

and a list of Task objects. How is it possible to get list of every Task as subtask by using stream(). I tried this one:

List<Task> subtasks = myTask.stream().map(x -> x.getSubtasks()).collect(Collectors.toList());

but it returns List<List<Task>>. What is the best way to join array from map() to existing result?

Use flatMap(x -> x.getSubtasks().stream()) instead of your map() — Robin Topper
– Robin Topper, Commented Apr 21, 2017 at 9:48
@Holger good point, missed that it's using Task inside Task. If the rabbit hole doesn't go deeper, that duplicate should do. — Kayaman
– Kayaman, Commented Apr 21, 2017 at 9:48

Zefick · Accepted Answer · 2017-04-21 09:49:00Z

2

    List<Task> subtasks = myTask.stream()
            .flatMap(x -> x.getSubtasks().stream())
            .collect(Collectors.toList());

answered Apr 21, 2017 at 9:49

Zefick

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