What is the main problem with the chosen solution structure? - Hard initialization of final fields - The structure does not guarantee the uniqueness of services in the cache - Service search complicates testing - No usage template. Strategy of flexibility. - Service locator complicates debugging Code: public class CarMaintenanceReminder { private final ServiceLocator serviceLocator; private final ReminderCache reminderCache; public CarMaintenanceReminder() { this.serviceLocator = new ServiceLocator(); this.reminderCache = new ReminderCache(); } public Reminder getOilChangeReminder(String carId) { Reminder reminder = reminderCache.getReminder(carId); if (reminder == null) { reminder = serviceLocator.getService(ReminderService.class).createOilChangeReminder(carId); reminderCache.addReminder(reminder); } return reminder; } } class ServiceLocator { public <T> T getService(Class<T> serviceClass) { return serviceClass.cast(generateService(serviceClass)); } private Object generateService(Class<?> serviceClass) { if (serviceClass == ReminderService.class) { return new ReminderService(); } return null; } } class Reminder { private final String carId; public Reminder(String carId) { this.carId = carId; } } class ReminderService { public Reminder createOilChangeReminder(String carId) { return new Reminder(carId); } } class ReminderCache { private final Map<String, Reminder> cache; public ReminderCache() { this.cache = new HashMap<>(); } public Reminder getReminder(String carId) { return cache.get(carId); } public void addReminder(Reminder reminder) { cache.put(reminder.getCarId(), reminder); } }

Main problems of the chosen solution structure:

• Rigid initialization of final fields: In the CarMaintenanceReminder class, services are created directly inside the constructor (new ServiceLocator(), new ReminderCache()), which makes it difficult to replace or mock these dependencies during testing and reduces flexibility.

• Structure does not guarantee the uniqueness of services in the cache: ServiceLocator creates a new instance of the service each time (new ReminderService()), instead of caching or using singletons. This can lead to excessive object creation and state management issues.

• Service lookup complicates testing: Using the service locator pattern hides the class dependencies, making understanding and testing more difficult, as dependencies are implicit and not passed explicitly.

• No usage pattern, strategy for flexibility: The absence of dependency injection patterns or configuration strategies reduces flexibility and extensibility.

• Service locator complicates debugging: Due to dynamic service retrieval via ServiceLocator, it is harder to trace which specific service is used, complicating debugging and maintenance.

It is recommended to use dependency injection through the constructor to explicitly pass necessary services, as well as to apply patterns that manage the lifecycle and uniqueness of services. For example:

public class CarMaintenanceReminder {
    private final ReminderService reminderService;
    private final ReminderCache reminderCache;

    public CarMaintenanceReminder(ReminderService reminderService, ReminderCache reminderCache) {
        this.reminderService = reminderService;
        this.reminderCache = reminderCache;
    }

    public Reminder getOilChangeReminder(String carId) {
        Reminder reminder = reminderCache.getReminder(carId);
        if (reminder == null) {
            reminder = reminderService.createOilChangeReminder(carId);
            reminderCache.addReminder(reminder);
        }
        return reminder;
    }
}

This approach improves testability, readability, and maintainability of the code.