Flat map demo

flap_map_Developer.java

package rs.dodalovic.streams.flap_map;

import java.util.List;

public class Developer {
    private final String name;
    private final List<String> programmingLanguages;

    public Developer(String name, List<String> programmingLanguages) {
        this.name = name;
        this.programmingLanguages = programmingLanguages;
    }

    public String getName() {
        return name;
    }

    public List<String> getProgrammingLanguages() {
        return programmingLanguages;
    }
}

flap_map_FlatMapMain.java

package rs.dodalovic.streams.flap_map;

import java.util.List;
import java.util.Set;
import java.util.function.Function;
import java.util.stream.Collectors;
import java.util.stream.Stream;

import static java.util.Arrays.asList;

public class FlatMapMain {

    private static final String JAVA = "Java";
    private static final String PHP = "Php";
    private static final String JAVASCRIPT = "Javascript";
    private static final String RUBY = "Ruby";
    private static final String SCALA = "Scala";
    private static final String PYTHON = "Python";
    private static final String CLOJURE = "Clojure";

    public static void main(String[] args) {

        final List<Developer> developers = asList(
                new Developer("John", asList(JAVA, PHP)),
                new Developer("Peter", asList(JAVA, PHP, JAVASCRIPT)),
                new Developer("Mike", asList(JAVA, PHP, CLOJURE)),
                new Developer("Steven", asList(JAVA, PHP, JAVASCRIPT, PYTHON)),
                new Developer("Kylie", asList(PHP, RUBY, SCALA)));

        final Set<String> supportedProgrammingLanguages = developers.stream()
                .flatMap(toLanguagesStream())
                .collect(Collectors.toSet());

        System.out.format("All supported languages: \n\n");
        supportedProgrammingLanguages.forEach(System.out::println);
    }

    private static Function<Developer, Stream<String>> toLanguagesStream() {
        return developer -> developer.getProgrammingLanguages().stream();
    }
}