Stream> instead of Stream

Question

I have a class Person having a set of Objects Contacts. I want to get a stream of Contacts from the stream of Persons.

public class Persons{
     private Set<Contact> contacts;
}

persons.stream().map(Person::getContacts);

gives me Stream<Set<Contact>> rather a Stream<Contact>

Any suggestion or help would be appreciated as I am quite new to Java 8 and Streams.

Why do you want to do this? Once you get the `Stream` you won't know which person each contact belongs to. — Klitos Kyriacou, Jan 26 '17 at 09:48

score 1 · Answer 1 · answered Jan 25 '17 at 19:13

1

You can achieve this by using Stream#flatMap instead of Stream#map. The JavaDoc shows an example of flattening a list of lines from a file to a list of words within each line. You can adapt the same technique to your domain model of Person and Contact.

answered Jan 25 '17 at 19:13

Chris Nauroth

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score 1 · Accepted Answer · edited May 23 '17 at 12:16

1

You may try this:

Stream<Contact> contacts = persons.stream().flatMap(p -> p.getContacts().stream());

or that:

Stream<Contact> contacts = persons.stream().map(Person::getContacts).flatMap(Set::stream);

Check this excellent thread so that you may understand the difference between map and flatMap.

edited May 23 '17 at 12:16

Community

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answered Jan 25 '17 at 19:16

Lachezar Balev

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2 Answers2