Sorting with Comparator

import java.util.*;
import java.util.stream.*;

class Demo {
    record User(String name, int age) {}

    void example() {
        var users = new ArrayList<>(List.of(
            new User("Alice", 30),
            new User("Bob",   25),
            new User("Cara",  30),
            new User("Dave",  25)
        ));

        // Single-key
        users.sort(Comparator.comparing(User::age));

        // Multi-key: age desc, then name asc
        users.sort(
            Comparator.comparing(User::age).reversed()
                .thenComparing(User::name)
        );
        users.forEach(System.out::println);

        // Sort stream → new list
        List<User> sorted = users.stream()
            .sorted(Comparator.comparing(User::name))
            .toList();

        // Null-safe comparisons
        users.sort(Comparator.comparing(User::name, Comparator.nullsLast(Comparator.naturalOrder())));
    }
}