Java | Фишки и трюки

public enum Day {
    MONDAY("понедельник"),
    TUESDAY("вторник"),
    WEDNESDAY("среда"),
    THURSDAY("четверг"),
    FRIDAY("пятница"),
    SATURDAY("суббота"),
    SUNDAY("воскресенье");
    
    Day(String value) {
        this.value = value;
    }
    
    String value;
    
    public String getValue() {
        return value;
    }

}

public class EnumClass {
    public static void main(String[] args) {
        System.out.println(message(Day.FRIDAY));
    }
    public static String message(Day day) {
        return "Это " + day.getValue();
        // Это пятница
    }
}

public class Quest {
    public static void main(String[] args) {
        System.out.println("5" + true);
    }
}

public class Quest {
    public static void main(String[] args) {
        System.out.println(5 + true);
    }
}

public class Quest {
    public static void main(String[] args) {
        System.out.println(calc());
    }

    static int calc() {
        try {
            if (1 == 1)
                throw new RuntimeException();
            return 1;
        } catch (Exception e) {
            return 2;
        } finally {
            return 3;
        }
    }
}

EntityManagerFactory emf = Persistence.createEntityManagerFactory("myPU");
EntityManager em = emf.createEntityManager();
em.getTransaction().begin();
Employee employee = new Employee("Jane", "Smith", 1200);
em.persist(employee);
em.getTransaction().commit();
em.close();

Session session = HibernateUtil.getSessionFactory().openSession();
session.beginTransaction();
Employee employee = new Employee("John", "Doe", 1000);
session.save(employee);
session.getTransaction().commit();
session.close();

Employee employee = employeeRepository.findById(1L).orElse(null);

<select id="selectEmployeeById" resultType="Employee">
    SELECT * FROM employees WHERE id = #{id}
</select>

import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;

@Service
public class UserService {

    private final UserRepository userRepository;

    public UserService(UserRepository userRepository) {
        this.userRepository = userRepository;
    }

    @Transactional
    public void updateUser(User user) {
        // Логика обновления пользователя в базе данных
        userRepository.save(user);
    }

    @Transactional(readOnly = true)
    public User getUserById(Long userId) {
        // Логика получения пользователя из базы данных
        return userRepository.findById(userId).orElse(null);
    }
}

public class SingletonExample {
    private static SingletonExample instance;

    private SingletonExample() {
        // Приватный конструктор
    }

    public static SingletonExample getInstance() {
        if (instance == null) {
            instance = new SingletonExample();
        }
        return instance;
    }
}

public class Counter {

    public static void main(String[] args) {
        int counter = 0;
        counter = counter++;
        System.out.println(counter);
    }

}