import java.util.Set;
import java.util.concurrent.ConcurrentMap;
import java.util.stream.Collectors;
import java.util.stream.Stream;

class Test {
    public static void main(String[] args) {
        Stream<String> ohMy = Stream.of("lions", "tigers", "bears").parallel();
        ConcurrentMap<Integer, String> map = ohMy
                .collect(Collectors.toConcurrentMap(String::length, k -> k,
                        (s1, s2) -> s1 + "," + s2));
        System.out.println(map); // {5=lions,bears, 6=tigers}
        System.out.println(map.getClass()); // java.util.concurrent.ConcurrentHashMap
    }
}