Java 8 stream returns list from element

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, Apr 21 '17 at 09:48
@Holger good point, missed that it's using `Task` inside `Task`. If the rabbit hole doesn't go deeper, that duplicate should do. — Kayaman, Apr 21 '17 at 09:48

score 2 · Accepted Answer · answered Apr 21 '17 at 09:49

2

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

answered Apr 21 '17 at 09:49

Zefick

1 Answers1