public abstract class AbstractService {

    public abstract String getName();

    public abstract void onCreate();

    public abstract void onDestroy();
}

======================================================================================================================================================================================================================================================

public abstract class DatabaseService extends AbstractService {

    private StorIOSQLite sqlite;

    public DatabaseService(StorIOSQLite sqlite) {
        this.sqlite = sqlite;
    }

    protected StorIOSQLite getSQLite() {
        return sqlite;
    }

    protected void releaseSQLiteReference() {
        this.sqlite = null;
    }
}

======================================================================================================================================================================================================================================================

public abstract class NetworkService<S> extends AbstractService {

    private Retrofit retrofit;

    private S service;

    public NetworkService(String baseUrl, OkHttpClient client) {
        this.retrofit = new Retrofit.Builder()
                .baseUrl(baseUrl)
                .addCallAdapterFactory(RxJava2CallAdapterFactory.create())
                .addConverterFactory(GsonConverterFactory.create(getGson()))
                .client(client)
                .build();
    }

    protected abstract S createService(Retrofit retrofit);

    protected abstract Gson getGson();

    protected void bindService() {
        this.service = createService(retrofit);
    }

    protected void unbindService() {
        this.service = null;
    }

    protected S getService() {
        return this.service;
    }
}

======================================================================================================================================================================================================================================================

public interface IServiceManager {

    void registerService(AbstractService service);

    void unregisterService(AbstractService service);

    boolean isServiceAvailable(String serviceName);

    AbstractService getService(String serviceName);
}

======================================================================================================================================================================================================================================================

public class ServiceManager implements IServiceManager {

    private static volatile IServiceManager instance;

    private static final Object singletonLock = new Object();

    private final ReentrantLock lock;

    private final Map<String, AbstractService> services;

    public static IServiceManager getInstance() {
        IServiceManager localInstance = instance;
        if(localInstance == null) {
            synchronized (singletonLock) {
                localInstance = instance;
                if(localInstance == null) {
                    localInstance = instance = new ServiceManager();
                }
            }
        }

        return localInstance;
    }

    private ServiceManager() {
        this.lock = new ReentrantLock();
        this.services = new HashMap<>(10, 0.4f);
    }

    @Override
    public void registerService(AbstractService service) {
        try {
            lock.lock();
            this.services.put(service.getName(), service);
            service.onCreate();
        } finally {
            lock.unlock();
        }
    }

    @Override
    public void unregisterService(AbstractService service) {
        try {
            lock.lock();
            this.services.remove(service.getName());
            service.onDestroy();
        } finally {
            lock.unlock();
        }
    }

    @Override
    public boolean isServiceAvailable(String serviceName) {
        try {
            lock.lock();
            return this.services.containsKey(serviceName);
        } finally {
            lock.unlock();
        }
    }

    @Override
    public AbstractService getService(String serviceName) {
        try {
            lock.lock();
            return this.services.get(serviceName);
        } finally {
            lock.unlock();
        }
    }
}