Given the definition of the Country class:

public class country {

public enum Continent {ASIA, EUROPE}

String name;

Continent region;

public Country (String na, Continent reg) {

name = na, region = reg;

}

public String getName () {return name;}

public Continent getRegion () {return region;}

}

and the code fragment:

List couList = Arrays.asList (

new Country ("Japan", Country.Continent.ASIA),

new Country ("Italy", Country.Continent.EUROPE),

new Country ("Germany", Country.Continent.EUROPE));

Map> regionNames = couList.stream ()

.collect(Collectors.groupingBy (Country ::getRegion,

Collectors.mapping(Country::getName, Collectors.toList()))));

System.out.println(regionNames);