Java tutorial
import java.util.NavigableSet; import java.util.TreeSet; public class CityNavigator { static NavigableSet<String> citiesSet; public static void main(String[] args) { String[] cities = { "A", "B", "C", "D", "E", "F" }; citiesSet = new TreeSet<String>(); for (String city : cities) citiesSet.add(city); } }