如何从不同的类访问同一个对象

Question

How can I have access to the same object from multiple classes?

I'm making a Java app for bookstore management using window builder, there are different types of users, and different panels for each user.

I need to have access to an updated object of the class bookStore (for example) to access the updated list of books, the list of users, so I can add or make changes on it. I took a look at singleton design pattern but I don't know if I can use it on this kind of situations. Should I use it? And if so, are there any cons?

Is there another way to do it?

Answer 1

Yes, you could use a singleton for that. The easiest way is to use Spring , declare your BookStore as a Bean in your Application class:

@Bean
public BookStore getBookStore(){
  return new BookStore();
}

And then, in every class where you need to reference it, declare your bookStore as an @Autowired object so Spring automatically finds your BookStore singleton and injects it. For example:

@Service
public class BookService {

  @Autowired
  private BookStore bookStore; //This variable will reference your BookStore singleton.

  public List<Book> getBooksFromStore(){
    return bookStore.getBooks();
  }

}

You can learn more about Spring here: https://www.baeldung.com/spring-tutorial

This is just an example so you can learn about singletons, but in a real world scenario you should use a database to persist your data, since the singleton will only hold data until your application stops executing.