1 import java.util.ArrayList; import java.util.Collections; import java.util.Comparator; import java.util.HashSet; import java.util.List; import java.util.Set; import java.util.TreeSet; import java.util.stream.Collectors; public class App { public static void main(String[ ] args) { Set<Integer> set = new HashSet<>(Set.of(5, 3, 2, 1, 4)); set = set.stream() .sorted() .collect(Collectors.toSet()); System.out.println(set); // => [1, 2, 3, 4, 5] TreeSet<Integer> treeSet = new TreeSet<>(Comparator.reverseOrder()); treeSet.addAll(set); System.out.println(treeSet); // => [5, 4, 3, 2, 1] } }