Design data structures for an online book reader system ~ KodeKnight

Design data structures for an online book reader system ~ KodeKnight
Design the data structures for an online book reader system.

public class Book {

    private long ID;

    private String details;

     

  

    public long getID() {

        return ID;

    }

  

    public Book(long id, String details) {

    }

}

public class User {

    private long ID;

    private String details;

    private int accountType;

    

    public long getID() {

        return ID;

    }

  

    public Book searchLibrary(long id) {

        return Book.find(id);

    }

  

    public void renewMembership() {

    }

}

Managing books :

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public class Books{  private Set<Book> books;     public void addBook(long iD, String details) {         books.add(new Book(iD, details));     }        public void update() {     }        public void delete(Book b) {         books.remove(b);     }        public Book find(long id) {         for (Book b : books)             if (b.getID() == id)                 return b;         return null;     } }

managing users : 

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public class Users {     private Set<User> users;        public Book searchLibrary(long id) {         return Book.find(id);     }        public void renewMembership() {     }        public static User find(long ID) {         for (User u : users) {             if (u.getID() == ID)                 return u;         }         return null;     }        public void addUser(long ID, String details,             int accountType) {         users.add(new User(ID, details, accountType));     }        public User(long iD, String details, int accountType) {     } }

Now we need the 1:1 mapping between book and user, which is managed by Book User, and online reader finally manages everything : 

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public class BookUsers {     private HashMap<Book,Set<User>> bookUsers;  private HashMap<User,Set<Book>> userBooks;     private void addUserToBookUserList(Book b, User u){   if(bookUsers.containsKey(b)){    Set<User> users = bookUsers.getValue(b);    users.add(u);   }else   {    bookUsers.add(b,new HashMap<User> (){u});   }  }     private void addBookToUserBookList(Book b, User u){   if(userBooks.containsKey(u)){    Set<Book> books = userBooks.getValue(u);    books.add(b);   }else   {    userBooks.add(u,new HashMap<Book> (){b});   }  }  public void assignBookToUser(Book b, User u)  {   addUserToBookUserList(b,u);   addBookToUserBookList(b,u);       } }    public class OnlineReaderSystem {     private Books books;     private Users users;  private BookUsers bookUsers;     private HashMap<Book,Set<User>> bookUsers;  private HashMap<User,Set<Book>> userBooks;     public void assignBookToUser()  {   bookUsers.assignBookToUser(b,u);       }        public OnlineReaderSystem(Books books, Users users) {     }        public void listenRequest() {     }        public Book searchBook(long ID) {         return books.find(ID);     }        public User searchUser(long ID) {         return users.find(ID);     }        public void display() {     }    }

Unfortunately, BookUser will change when we take into account db relational model, as we dont have to keep things in-memory. 
https://xmruibi.gitbooks.io/interview-preparation-notes/content/OOD/DesignExamples/OnlineReader.html

This question comes from the book named "Cracking Code Interview", Chapter 7; It is very easy problem with thinking about the insert/remove/update/retrieve action.

Functionality

• User Membership Creation and Extension
• Search the book in memory
• Reading the book

Objects

• Book:
  • ID
  • Title
  • Author
  • Content
  • Method
    • showContent
• Books: (In-memory storage for many book objects)
  • Set
  • Method
    • find
    • add
    • delete
    • update
• User
  • ID
  • Name
  • accoutnType
  • Method
    • findBook
    • read (book.showContent)
• Users
  • Set
  • Method
    • find
    • add
    • delete
    • update

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