Before: Duplicated Logic Example

public class PasswordChangeNotifier {
    public void sendNotification(User user) {
        User loadedUser = userRepository.findById(user.getId());
        boolean notify = loadedUser.getSettings().isPasswordChangeEnabled();
        if (notify) {
            emailService.send(
                user.getEmail(),
                "Password Changed",
                "Your password was changed at " + new Date()
            );
        }
        auditLogService.log("Password change notification sent to " + user.getId());
    }
}

public class OrderConfirmationNotifier {
    public void sendNotification(User user, Order order) {
        User loadedUser = userRepository.findById(user.getId());
        boolean notify = loadedUser.getSettings().isOrderConfirmationEnabled();
        if (notify) {
            emailService.send(
                user.getEmail(),
                "Order Confirmed: " + order.getId(),
                "Your order for " + order.getItems() + " is confirmed"
            );
        }
        auditLogService.log("Order confirmation sent to " + user.getId());
    }
}

After: Abstract Service Implementation

public abstract class AbstractNotifier {
    protected final UserRepository userRepository;
    protected final EmailService emailService;
    protected final AuditLogService auditLogService;

    public AbstractNotifier(UserRepository userRepository,
                          EmailService emailService,
                          AuditLogService auditLogService) {
        this.userRepository = userRepository;
        this.emailService = emailService;
        this.auditLogService = auditLogService;
    }

    public final void sendNotification(User user, Object context) {
        User loadedUser = userRepository.findById(user.getId());
        if (isNotificationEnabled(loadedUser, context)) {
            emailService.send(
                getRecipient(loadedUser),
                getSubject(context),
                getBody(loadedUser, context)
            );
        }
        auditLogService.log(getLogMessage(loadedUser, context));
    }

    protected abstract boolean isNotificationEnabled(User user, Object context);
    protected abstract String getRecipient(User user);
    protected abstract String getSubject(Object context);
    protected abstract String getBody(User user, Object context);
    protected abstract String getLogMessage(User user, Object context);
}

public class PasswordChangeNotifier extends AbstractNotifier {
    @Override protected boolean isNotificationEnabled(User user, Object context) {
        return user.getSettings().isPasswordChangeEnabled();
    }
    // Other method implementations...
}