TreeSet example

    public static void main(String[] args) {
        TreeSet<Person> people = new TreeSet<>();
        people.add(new Person(LocalDateTime.of(1987, 5, 14, 0, 0)));
        people.add(new Person(LocalDateTime.of(2000, 5, 14, 0, 0)));
        people.add(new Person(LocalDateTime.of(2002, 5, 14, 0, 0)));

        System.out.println("people: " + people);
        NavigableSet<Person> reversedPeople = people.descendingSet();
        System.out.println("Reversed people: " + reversedPeople);
    }

    public static class Person implements Comparable<Person> {
        private final LocalDateTime birthday;

        public Person(LocalDateTime birthday) {
            this.birthday = birthday;
        }

        @Override
        public int compareTo(Person o) {
            return this.birthday.compareTo(o.birthday);
        }

        @Override
        public String toString() {
            return "Person{" +
                    "birthday=" + birthday +
                    '}';
        }
    }