@Service
@RequiredArgsConstructor
public class UserService {

    private final UserRepository userRepository;

    @Transactional(readOnly = true)
    public UserDto getUser(Long id) {
        User user = userRepository.findById(id)
            .orElseThrow(() -> new EntityNotFoundException("User not found"));
        return UserDto.from(user);
    }
}

@Component
public class OrderService {
    @Autowired
    private ApplicationEventPublisher publisher;

    public void createOrder(Order order) {
        // 1. Сохраняем заказ
        orderRepository.save(order);

        // 2. Публикуем ивент
        publisher.publishEvent(new OrderCreatedEvent(order));
        // 3. До выхода из метода все @EventListener уже будут выполнены
    }
}

@EventListener
public void sendEmail(OrderCreatedEvent event) {
    emailService.sendConfirmation(event.getOrder());
}

@Async
@EventListener
public void sendEmail(OrderCreatedEvent event) {
    emailService.sendConfirmation(event.getOrder());
}

@EnableAsync
@Configuration
public class AsyncConfig {}

@Component
@Lazy
public class HeavyComponent {
    public HeavyComponent() {
        System.out.println("HeavyComponent инициализирован");
    }
}

@Component
public class SomeService {
    private final HeavyComponent heavy;

    public SomeService(@Lazy HeavyComponent heavy) {
        this.heavy = heavy;
    }
}

spring:
  main:
    lazy-initialization: true

for (int i = 0; i < 5; i++) {
   if (i == 2) {
       continue;  // Skip iteration when i is 2
   }
   if (i == 4) {
       break;     // Exit loop when i is 4
   }
   System.out.println(i);
}

class Calculator {
   int add(int a, int b) {
       return a + b;
   }
   double add(double a, double b) {
       return a + b;
   }
}

var list = new ArrayList<String>();
list.add("Hello");
list.add("Java");

// Компилятор понимает, что list -> ArrayList<String>

public class CircleCalculator {
   private final double PI = 3.14159;
   public double calculateArea(double radius) {
       return PI * radius * radius;
   }
}