JorgeCastilloPrz

public class ApplicationClass extends Application {

    private ObjectGraph objectGraph;

    @Override
    public void onCreate() {
        super.onCreate();
        objectGraph = ObjectGraph.create(getModules().toArray());
        objectGraph.inject(this);
    }

JorgeCastilloPrz

public void BookController {
    
    private static BookController instance = null;
    private BookRepository bookRepository = new PersistentBookRepository();
    
    protected BookController() {}

    public static BookController getInstance() {
        if(instance == null) {
            instance = new BookController();

JorgeCastilloPrz

public interface BookRepository {
  public List<Book> getAllBooks();
  public List<Book> getAllBooksFromUser(int userId);
  public List<Book> getAllBooksByCategory(BookCategory category);
  public Book getBook(int bookId);
  public Book getBookByName(String bookName);
  public void removeBook(int bookId);
  public void markAsCompleted(int bookId);
}