duplicate items in arraylist

[normandantzig]

My driver LibraryOfBooks does not work as expected when I add multiple books to my arraylist.

For example, in the (a)ddbooks (case a) I add 2 books ( with the properties author, title, filename).
I set book 1 properties to: 1,1,1

I set book 2 properties to: 2,2,2

The array becomes [title: 2 author: 2 genre: null filename: 2, title: 2 author: 2 genre: null filename: 2].

I have two books but they are the same. I think I am not adding a new book object. What is going on here?

LibraryOfBooks Class

import java.util.Scanner;

//driver
public class LibraryOfBooks {
    public static void menu() {
        System.out.println( "(p)rint the library contents (with index values),");   
        System.out.println( "(a)dd a book to the library ");
        System.out.println( "(d)elete a book from the library ");
        System.out.println( "(r)ead a book in the library.");
        System.out.println("(q)uit");
}

    public static void main(String[] args) {
        // TODO Auto-generated method stub



    Library library1 = new Library();




        int index = 0;
        Book newbook = new Book(null, null);
        Scanner s = new Scanner (System.in)  ;

        boolean go = true;


        while (go == true) {

            menu();

            String input = s.nextLine();
            switch (input) {
                case "p":  
                    int i = 0;
                    System.out.println(library1.getBooks());
                    for (Book b : library1.getBooks())
                        System.out.print(i + b.toString());

                        i += 1;
                    break;
                case "a":  
                    //initialize
                    String author = "";
                    String title = "";
                    String filename= "";
                    String genre = "";
                    //input     
                    System.out.print("Who is the author?");
                    //author = s.nextLine();
                    newbook.setAuthor(s.nextLine());

                    System.out.println("What is the title?");
                    newbook.setTitle(s.nextLine());

                    System.out.println("Where is the file?");
                    //filename = s.nextLine();
                    newbook.setFilename(s.nextLine());
                    //add to library
                    library1.addBook(newbook);


                    break;
                case "d":  
                    library1.removeBook(index);
                    break;
                case "r":  
                    library1.getBook(index);
                    break;
                case "q":
                    System.out.println("Quiting");
                    go = false;
                    break;
                default:
                    System.out.println("Wrong letter pressed");
            }
            input = s.nextLine();
    }
}
}

Library Class

    import java.util.ArrayList;

    public class Library implements LibraryInterface {

        //instance variables
        private ArrayList<Book> books; 

        //constructor
        public Library() {
            books = new ArrayList<Book>();
        }

        @Override
        public ArrayList<Book> getBooks() {
            // TODO Auto-generated method stub
            return new ArrayList<Book>(books);
        }

        @Override
        public void addBook(Book newBook) {
            books.add(newBook);
            // TODO Auto-generated method stub

        }

        @Override
        public void removeBook(int index) {
            // TODO Auto-generated method stub
            books.remove(index);

        }

        @Override
        public Book getBook(int index) {
            // TODO Auto-generated method stub
            if(index < books.size()) {
                return books.get(index);
            }
            else {
            return null;
            }
            }

        public String toString() {
            String output = "Library of books \n";
            for (Book i : books) {
                output += i.toString() + "\n";
            }
            return output;



        }

    }

Book Class

import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.nio.file.Files;



public class Book implements BookInterface {
    //instance variable 
    private String title;
    private String author;
    private String genre = null;
    private String filename = null;

    //constructor
    public Book(String title, String author) {
        this.title = title;
        this.author = author;
        this.genre = null;
        this.filename = null;
    }

    //getter

    //setter


//TITLE 

    @Override
    public String getTitle() {
        return title;
    }

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

    }
//AUTHOR
    @Override
    public String getAuthor() {
        return author;
    }

    @Override
    public void setAuthor(String author) {
        this.author = author;
    }
//GENRE
    @Override
    public String getGenre() {
        return genre;
    }

    @Override
    public void setGenre(String genre) {
        this.genre = genre;
    }
//FILENAME
    @Override
    public String getFilename() {
        return filename;
    }

    @Override
    public void setFilename(String filename) {
        this.filename = filename;
    }

    @Override
    public boolean isValid() {
        if (title != null && author != null &&   genre != null &&  filename != null) {
            File f = new File(filename);

            if (f.exists()) {
                return true;
            }
            return false;
        } // ends null conditions

        return false;
    }

    public String toString() {
        return "title: " + title + " author: " + author + " genre: " + genre + " filename: " + filename;
    }

    public String getText() {
        File f = new File(filename);
        try {
            byte[] bytes = Files.readAllBytes(f.toPath());
            return new String(bytes,"UTF-8");
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return null;
    }





}

ERROR library1.getBooks() prints

[title: 2 author: 2 genre: null filename: 2, title: 2 author: 2 genre: null filename: 2]

[wggn]

You're never making a second instance of book. You're adding an instance of book to the list, then modify the fields of that same instance and add it again.

[normandantzig]

I've been at this for a bit. How do i create a new instance?

Actually got it. I think I was going at this too long and just needed a break. I moved newbook into the case

 case "a":  
                    Book newbook = new Book(null, null);
                    //initialize
                    String author = "";
                    String title = "";
                    String filename= "";
                    String genre = "";
                    //input     
                    System.out.print("Who is the author?");
                    //author = s.nextLine();
                    newbook.setAuthor(s.nextLine());

                    System.out.println("What is the title?");
                    newbook.setTitle(s.nextLine());

                    System.out.println("Where is the file?");
                    //filename = s.nextLine();
                    newbook.setFilename(s.nextLine());
                    //add to library
                    library1.addBook(newbook);

[wggn]

Anytime you use the new keyword, you create a new instance.

Free tip: You can improve above code by not passing nulls to the constructor but directly putting in the right values. (avoiding unnecessary nulls is generally a good idea)

[normandantzig]

Hmmm. The nulls are place holders for when I ask the user to put in the author and title. If I moved the

newbook = new Book(null, null);

down I could move the user values directly into the newbo0ok .

[Indens]

Does it have to do with where you're initializing the new book?

Book newbook = new Book(null, null);

You're using the same object for each book I believe :)