FlatMapStreamTest.java

/**
 * Copyright (c) 2016 Marco Velluto
 * @since Java 1.8
 * @dependency: <groupId>joda-time</groupId>
 */

import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
import java.util.stream.Collectors;

import org.junit.Assert;
import org.junit.Test;


public class FlatMapTest
{
    @Test
    public void flatMap()
    {
        List<Developer> team = new ArrayList<>();
        Developer polyglot = new Developer("esoteric");
        polyglot.add("clojure");
        polyglot.add("scala");
        polyglot.add("groovy");
        polyglot.add("go");

        Developer busy = new Developer("pragmatic");
        busy.add("java");
        busy.add("javascript");

        team.add(polyglot);
        team.add(busy);

        List<String> teamLanguages = team.stream().map(developer -> developer.getLanguages()).flatMap(list -> list.stream())
                                         .collect(Collectors.toList());
        Assert.assertTrue(teamLanguages.containsAll(polyglot.getLanguages()));
        Assert.assertTrue(teamLanguages.containsAll(busy.getLanguages()));
    }

    private class Developer
    {
        private String name;
        private Set<String> languages;

        public Developer(String name)
        {
            this.languages = new HashSet<>();
            this.name = name;
        }

        public void add(String language)
        {
            this.languages.add(language);
        }

        public Set<String> getLanguages()
        {
            return languages;
        }

        public String getName()
        {
            return name;
        }

        public void setName(String name)
        {
            this.name = name;
        }

        public void setLanguages(Set<String> languages)
        {
            this.languages = languages;
        }
    }
}