Question

I have a ShoppingCart app that can add/remove Book objects
A book has an isbn attribute.
I need to check if someone has added a duplicate copy of same book to the cart
ie,

Book b1 = new Book("isbn222");
Book b2 = new Book("isbn222");
Book b3 = new Book("isbn333");
Book b4 = new Book("isbn444");
Book b5 = new Book("isbn444");
Book b6 = new Book("isbn444");
Book b7 = new Book("isbn555");
//add these to cart

In this case I want to generate a warning to the user that duplicates 2 copies with isbn222, three copies with isbn444 are added.
I thought of creating a CartValidator as below,However,I couldn’t implement the logic given below..How do you create sub lists in java?
Any help regarding this much appreciated.

thanks

mark.

public class CartValidator {
    public static String validate(ShoppingCart<Book> cart) {
        StringBuffer warning = new StringBuffer("duplicates");
        List<Book> items = cart.getItems();

        /*
         * take first item from list,       temp= items.get(0)
         * check against all the rest for duplicates and build warning  compare with item1,item2..
         * take second item                 temp= items.get(1)
         * check against all the rest for duplicates and build warning   compare with item2,item3..
         */

        return warning.toString();

}

Answer 1

I would suggest to have Map with <String, List<Book>>. where String key the Book ISBN and the list is the books with the ISBN.