Turn a stream of objects into a linked list of attributes

Question

My goal: Take a LinkedList of Users and extract a LinkedList of their usernames in an elegant, Java-8 way.

public static void main(String[] args) {

    LinkedList<User> users = new LinkedList<>();
    users.add(new User(1, "User1"));
    users.add(new User(2, "User2"));
    users.add(new User(3, "User3"));

    // Vanilla Java approach
    LinkedList<String> usernames = new LinkedList<>();
    for(User user : users) {
        System.out.println(user.getUsername());
        usernames.add(user.getUsername());
    }
    System.out.println("Usernames = " + usernames.toString());

    // Java 8 approach
    users.forEach((user) -> System.out.println(user.getUsername()));
    LinkedList<String> usernames2 = users.stream().map(User::getUsername). // Is there a way to turn this map into a LinkedList?
    System.out.println("Usernames = " + usernames2.toString());
}

static class User {
    int id;
    String username;

    public User() {
    }

    public User(int id, String username) {
        this.id = id;
        this.username = username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getUsername() {
        return username;
    }

    public int getId() {
        return id;
    }
}

I am stuck trying to convert the Stream object into a LinkedList. I could turn it into an array (Stream::toArray()) and turn that into a List (Arrays.asList(Stream::toArray())) but that just seems so... no thank you.

Am I missing something?

Answer 1

You can use a Collector like this to put the result into a LinkedList:

LinkedList<String> usernames2 = users.stream()
                                .map(User::getUsername)
                                .collect(Collectors.toCollection(LinkedList::new));