Java code problem

Question

Hi !
I have a little problem.
My program has 4 classes: Book, Library, View and controller.
Class Book{
   Private String bName, author;
          Book(bName, author){}
// methods
  public String toString(){}
class Library{
    Book[] bok;
    int nbrOfBook;
// constructor
public void addBook(Book )
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// this class shows all books with help of addBook and toString from class Book.
class View {
  Book [] aBok;
Library library;
class Controller{
    Library library;
    View v;
Controller(Library, View){ }
  }when user want to add a new book, the controller object must controll it and the veiw object must show this book beside other books(to uppdate the view object).
The Book, Library and View classes are ok.
But I have just problem with controller class , how the controller object controls other objects.

Answer 1

If the library would offer an event mechanism, the view(s) could register for events. You could achieve this with the Observer/Observable classes, with PropertyChangeSupport (that wouldn't work well with collections) or with something you'd write yourself (depending on your experience, I'd start with Observer/Observable).
But how would the views get a hold of the library? Not via the controller IMO - you should be able to transparently add or remove views without changing either model (library) or controller. The best way (again, IMHO) would be to make library a singleton, so that both view(s) and controller can look up the library without passing it around. (I assume a standalone application here - for other contexts the same principle applies, but sometimes static is a bad idea.)
By the way, I'm not sure if that's your actual code, but it wouldn't compile, of course (with the Class, Private and stuff).