List<String> source = new ArrayList<>();
source.add("Java");

List<String> view = Collections.unmodifiableList(source);
List<String> copy = List.copyOf(source);

source.add("Spring");

System.out.println(view); // [Java, Spring]
System.out.println(copy); // [Java]

public List<String> getUsers() {
    return List.copyOf(users);
}

Path a = Path.of("data.txt");
Path b = Path.of("./data.txt");

System.out.println(a.equals(b)); // false

boolean same = Files.isSameFile(a, b);

Path file = Path.of("data.txt");
Path link = Path.of("data-link.txt");

Files.isSameFile(file, link); // true, если link ведёт к data.txt

CompletableFuture<User> future =
        CompletableFuture.supplyAsync(() -> userClient.loadUser(id));

private static final ExecutorService IO_POOL =
        Executors.newFixedThreadPool(32);

CompletableFuture<User> future =
        CompletableFuture.supplyAsync(
                () -> userClient.loadUser(id),
                IO_POOL
        );

IO_POOL.shutdown();

future.thenApplyAsync(
        user -> enrichUser(user),
        IO_POOL
);

private static final Map<Class<?>, Metadata> CACHE =
        new ConcurrentHashMap<>();

private static final ClassValue<Metadata> CACHE =
        new ClassValue<>() {
            @Override
            protected Metadata computeValue(Class<?> type) {
                return buildMetadata(type);
            }
        };

Metadata metadata = CACHE.get(MyClass.class);

static ConcurrentHashMap<Class<?>, ...>

users.parallelStream()
     .map(this::callExternalApi)
     .toList();

ExecutorService executor =
    Executors.newFixedThreadPool(20);

List<Item> small = hugeList.subList(0, 10);
hugeList = null;

List<Item> small = new ArrayList<>(hugeList.subList(0, 10));

жалоба → эмбеддинг → DeepNetts → срочность 0–10

var ids = new HashSet<Integer>(1_000_000);

for (int i = 0; i < 10; i++) {
    ids.add(i);
}

for (int id : ids) {
    process(id);
}

ids = new HashSet<>(ids);