Java Interview Questions

public Builder withName(String name) {
    this.name = name;
    return this;
}

outerLoop:
for (int i = 0; i < 10; i++) {
    for (int j = 0; j < 10; j++) {
        if (someCondition) break outerLoop;
    }
}

try (var conn = dataSource.getConnection();
     var stmt = conn.prepareStatement(sql)) {
    // use resources
} // auto-closed in reverse order, even if exception occurs

try { return 1; }
finally { return 2; } // returns 2, silently discards 1

public User findById(long id) throws UserNotFoundException {
    try {
        return jdbc.query(...);
    } catch (EmptyResultDataAccessException e) {
        throw new UserNotFoundException(id, e); // chained
    }
}

volatile boolean running = true;
// Thread 1
while (running) { /* work */ }
// Thread 2
running = false; // Thread 1 sees this immediately

// Chaining with map/flatMap
String city = user.getAddress()
    .flatMap(Address::getCity)
    .map(String::toUpperCase)
    .orElse("UNKNOWN");

// orElseGet for lazy default (computed only if empty)
User user = repo.findById(id).orElseGet(() -> createDefault());

// orElseThrow for mandatory values
User user = repo.findById(id)
    .orElseThrow(() -> new UserNotFoundException(id));

Predicate<String> isLong = s -> s.length() > 10;
Predicate<String> startsWithA = s -> s.startsWith("A");
Predicate<String> combined = isLong.and(startsWithA);

@Service
public class OrderService {
    private final PaymentGateway paymentGateway;
    private final OrderRepository orderRepository;

    // @Autowired is optional with single constructor
    public OrderService(PaymentGateway paymentGateway,
                        OrderRepository orderRepository) {
        this.paymentGateway = paymentGateway;
        this.orderRepository = orderRepository;
    }
}

public class Singleton {
    private static volatile Singleton instance;
    public static Singleton getInstance() {
        if (instance == null) {
            synchronized (Singleton.class) {
                if (instance == null) {
                    instance = new Singleton();
                }
            }
        }
        return instance;
    }
}

User user = User.builder()
    .name("Alice")
    .email("alice@example.com")
    .age(30)
    .active(true)
    .build();

record Email(String value) {
    Email { // compact constructor
        if (!value.contains("@"))
            throw new IllegalArgumentException("Invalid email");
    }
}