Path src = Path.of("data.csv");
Path backup = Path.of("data.csv.bak");

Files.copy(src, backup, StandardCopyOption.REPLACE_EXISTING);

data.csv → data.csv.bak

String a = null;
String b = "hi";

boolean result = a.equals(b); // NullPointerException

boolean result = Objects.equals(a, b); // false

Objects.equals(null, null);   // true
Objects.equals("hi", "hi");   // true
Objects.equals("hi", null);   // false

@Override
public boolean equals(Object o) {
    if (this == o) return true;
    if (!(o instanceof User user)) return false;

    return Objects.equals(id, user.id)
            && Objects.equals(email, user.email);
}

boolean sameMinute =
    first.truncatedTo(ChronoUnit.MINUTES)
         .equals(second.truncatedTo(ChronoUnit.MINUTES));

ChronoUnit.HOURS
ChronoUnit.DAYS

users.stream()
    .peek(System.out::println)
    .toList();

runtimeOnly("org.springframework.boot:spring-boot-properties-migrator")

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-properties-migrator</artifactId>
    <scope>runtime</scope>
</dependency>

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

private final AtomicLong requests = new AtomicLong();

requests.incrementAndGet();

private final LongAdder requests = new LongAdder();

requests.increment();

AtomicLong:

Thread 1 ─┐
Thread 2 ─┼──> [100000]
Thread 3 ─┘


LongAdder:

Thread 1 → [10]
Thread 2 → [20]
Thread 3 → [15]

              ↓
            sum()

adder.sum()

restTestClient.get()
        .uri("/api/users/42")
        .exchange()
        .expectStatus().isOk()
        .expectBody(User.class)
        .value(user -> assertThat(user.id()).isEqualTo(42));

@AutoConfigureRestTestClient

if (animal instanceof Dog) {
    Dog d = (Dog) animal;
    d.bark();
}

if (animal instanceof Dog d) {
    d.bark();
}

Map<List<Integer>, String> map = new HashMap<>();

List<Integer> key = new ArrayList<>(List.of(1, 2));

map.put(key, "Ritesh");

key.add(3);

System.out.println(map.get(key));

Ritesh

CountDownLatch done = new CountDownLatch(1);

done.await();      // ждём сигнал
done.countDown();  // работа завершена

ScheduledExecutorService exec =
    Executors.newSingleThreadScheduledExecutor();

exec.scheduleAtFixedRate(
    this::doWork,
    0,
    1,
    TimeUnit.SECONDS
);

Thread.sleep() хорошо подходит для простой задержки.

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

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