References

https://www.geeksforgeeks.org/design-an-online-book-reader-system/

Features

Searching the database of books and reading a book.
User membership creation and extension.
Only one active user at a time and only one active book by this user

Entity

OnlineReaderSystem
Book
User, UserManager
Library
Display

Code for test

public class AppTest { 

    public static void main(String[] args) 
    { 

        OnlineReaderSystem onlineReaderSystem = new OnlineReaderSystem(); 

        Book dsBook = new Book(1, "It contains Data Structures", "Ds"); 
        Book algoBook = new Book(2, "It contains Algorithms", "Algo"); 

        onlineReaderSystem.getLibrary().addBook(dsBook); 
        onlineReaderSystem.getLibrary().addBook(algoBook); 

        User user1 = new User(1, " ", "Ram"); 
        User user2 = new User(2, " ", "Gopal"); 

        onlineReaderSystem.getUserManager().addUser(user1); 
        onlineReaderSystem.getUserManager().addUser(user2); 

        onlineReaderSystem.setActiveBook(algoBook); 
        onlineReaderSystem.setActiveUser(user1); 

        onlineReaderSystem.getDisplay().turnPageForward(); 
        onlineReaderSystem.getDisplay().turnPageForward(); 
        onlineReaderSystem.getDisplay().turnPageBackward(); 
    } 
}

Code for class

import java.util.HashMap; 

/* 
* This class represents the system 
*/

class OnlineReaderSystem { 
    private Library library; 
    private UserManager userManager; 
    private Display display; 
    private Book activeBook; 
    private User activeUser; 

    public OnlineReaderSystem() 
    { 
        userManager = new UserManager(); 
        library = new Library(); 
        display = new Display(); 
    } 

    public Library getLibrary() 
    { 
        return library; 
    } 

    public UserManager getUserManager() 
    { 
        return userManager; 
    } 

    public Display getDisplay() 
    { 
        return display; 
    } 

    public Book getActiveBook() 
    { 
        return activeBook; 
    } 

    public void setActiveBook(Book book) 
    { 
        activeBook = book; 
        display.displayBook(book); 
    } 

    public User getActiveUser() 
    { 
        return activeUser; 
    } 

    public void setActiveUser(User user) 
    { 
        activeUser = user; 
        display.displayUser(user); 
    } 
} 

/* 
* We then implement separate classes to handle the user 
* manager, the library, and the display components  
*/

/* 
* This class represents the Library which is responsible 
* for storing and searching the books. 
*/
class Library { 
    private HashMap<Integer, Book> books; 

    public Library() 
    { 
        books = new HashMap<Integer, Book>(); 
    } 

    public Boolean addBook(int id, String details, String title) 
    { 
        if (books.containsKey(id)) { 
            return false; 
        } 
        Book book = new Book(id, details, title); 
        books.put(id, book); 
        return true; 
    } 

    public Boolean addBook(Book book) 
    { 
        if (books.containsKey(book.getId())) { 
            return false; 
        } 

        books.put(book.getId(), book); 
        return true; 
    } 

    public boolean remove(Book b) 
    { 
        return remove(b.getId()); 
    } 

    public boolean remove(int id) 
    { 
        if (!books.containsKey(id)) { 
            return false; 
        } 
        books.remove(id); 
        return true; 
    } 

    public Book find(int id) 
    { 
        return books.get(id); 
    } 
} 

/* 
* This class represents the UserManager which is responsible  
* for managing the users, their membership etc. 
*/

class UserManager { 
    private HashMap<Integer, User> users; 

    public UserManager() 
    { 
        users = new HashMap<Integer, User>(); 
    } 
    public Boolean addUser(int id, String details, String name) 
    { 
        if (users.containsKey(id)) { 
            return false; 
        } 
        User user = new User(id, details, name); 
        users.put(id, user); 
        return true; 
    } 

    public Boolean addUser(User user) 
    { 
        if (users.containsKey(user.getId())) { 
            return false; 
        } 

        users.put(user.getId(), user); 
        return true; 
    } 

    public boolean remove(User u) 
    { 
        return remove(u.getId()); 
    } 

    public boolean remove(int id) 
    { 
        if (users.containsKey(id)) { 
            return false; 
        } 
        users.remove(id); 
        return true; 
    } 

    public User find(int id) 
    { 
        return users.get(id); 
    } 
} 

/* 
* This class represents the Display, which is responsible  
* for displaying the book, it's pages and contents. It also  
* shows the current user. * It provides the method 
* turnPageForward, turnPageBackward, refreshPage etc. 
*/

class Display { 
    private Book activeBook; 
    private User activeUser; 
    private int pageNumber = 0; 

    public void displayUser(User user) 
    { 
        activeUser = user; 
        refreshUsername(); 
    } 

    public void displayBook(Book book) 
    { 
        pageNumber = 0; 
        activeBook = book; 

        refreshTitle(); 
        refreshDetails(); 
        refreshPage(); 
    } 

    public void turnPageForward() 
    { 
        pageNumber++; 
        System.out.println("Turning forward to page no " + 
                   pageNumber + " of book having title " + 
                                     activeBook.getTitle()); 
        refreshPage(); 
    } 

    public void turnPageBackward() 
    { 
        pageNumber--; 
        System.out.println("Turning backward to page no " + 
                    pageNumber + " of book having title " +  
                                    activeBook.getTitle()); 
        refreshPage(); 
    } 

    public void refreshUsername() 
    { 
        /* updates username display */
        System.out.println("User name " + activeUser.getName() +  
                                             " is refreshed"); 
    } 

    public void refreshTitle() 
    { 
        /* updates title display */
        System.out.println("Title of the book " + 
                        activeBook.getTitle() + " refreshed"); 
    } 

    public void refreshDetails() 
    { 
        /* updates details display */
        System.out.println("Details of the book " + 
                        activeBook.getTitle() + " refreshed"); 
    } 

    public void refreshPage() 
    { 
        /* updated page display */
        System.out.println("Page no " + pageNumber + " refreshed"); 
    } 
} 

/*  
* The classes for User and Book simply hold data and  
* provide little functionality. 
* This class represents the Book which is a simple POJO 
*/

class Book { 
    private int bookId; 
    private String details; 
    private String title; 

    public Book(int id, String details, String title) 
    { 
        bookId = id; 
        this.details = details; 
        this.title = title; 
    } 

    public int getId() 
    { 
        return bookId; 
    } 

    public void setId(int id) 
    { 
        bookId = id; 
    } 

    public String getDetails() 
    { 
        return details; 
    } 

    public void setDetails(String details) 
    { 
        this.details = details; 
    } 

    public String getTitle() 
    { 
        return title; 
    } 

    public void setTitle(String title) 
    { 
        this.title = title; 
    } 
} 

/* 
* This class represents the User which is a simple POJO 
*/

class User { 
    private int userId; 
    private String name; 
    private String details; 

    public void renewMembership() 
    { 
    } 

    public User(int id, String details, String name) 
    { 
        this.userId = id; 
        this.details = details; 
        this.name = name; 
    } 

    public int getId() 
    { 
        return userId; 
    } 

    public void setId(int id) 
    { 
        userId = id; 
    } 

    public String getDetails() 
    { 
        return details; 
    } 

    public void setDetails(String details) 
    { 
        this.details = details; 
    } 

    public String getName() 
    { 
        return name; 
    } 

    public void setName(String name) 
    { 
        this.name = name; 
    } 
}

interview-preparation / what-we-do

[Object-Oriented Design] interview questions #5 #112

References

Features

Entity

Code for test

Code for class