Java 8 lambda create list of Strings from list of custom class objects

Question

I have the following qustion:

How can I convert the following code snipped to Java 8 lambda style?

List<String> tmpAdresses = new ArrayList<String>();
for (User user : users) {
    tmpAdresses.add(user.getAdress());
}

Have no idea and started with the following:

List<String> tmpAdresses = users.stream().map((User user) -> user.getAdress());

Carrew

You're almost there. Assuming your map lambda returns a String just add .collect(Collectors.toList()) to map(...). – Dacosta

Note: (User user) -> user.getAddress() can be written as user -> user.getAddress() or just User::getAddress – Escent

Answer 1

You need to collect your Stream into a List:

List<String> adresses = users.stream()
    .map(User::getAdress)
    .collect(Collectors.toList());

For more information on the different Collectors visit the documentation.

User::getAdress is just another form of writing (User user) -> user.getAdress() which could as well be written as user -> user.getAdress() (because the type User will be inferred by the compiler)

Inclinometer

Answer 2

It is extended your idea:

List<String> tmpAdresses = users.stream().map(user ->user.getAdress())
.collect(Collectors.toList())

Airy

You should add a new answer if its better/ alternative than the other one. Explain how its better. – Succession

Answer 3

One more way of using lambda collectors like above answers

 List<String> tmpAdresses= users
                  .stream()
                  .collect(Collectors.mapping(User::getAddress, Collectors.toList()));

Saeger

Answer 4

You are almost there, you just need to collect streams in a List.

 List<String> addressList =
  users
    .stream()
    .map(user -> user.getAddress())
    .collect(Collectors.toList())

Maladroit

How is your answer different to the already existing ones posted 5 years ago? – Inclinometer

I am new here, just want to contribute more and more. That's why I didn't check the timing of previous answers. – Maladroit

You should check whether your answer is different from other answers, we don't want 50 answers to one question where all are saying the exact same thing. If you want to contribute I invite you to search for unanswered questions (e.g. for the java tag) directly. – Inclinometer

Okay, thanks @Lino. Will surely search for unanswered questions, and try to give solutions. – Maladroit

Answer 5

You can use this to convert Long to String:

List<String> ids = allListIDs.stream()
                             .map(listid-> String.valueOf(listid))
                             .collect(Collectors.toList());

Khorma

This doesn't attempt to answer the OPs question, though. OP is explicitly asking to map a User to its adress. Also how is your question different to the already existing ones? – Inclinometer