public void showBooks(Map books) {
        Book book = null;
        Object counter;

        Iterator inter = books.entrySet().iterator();
        while (inter.hasNext()) {
            Map.Entry entry = (Map.Entry) inter.next();
            counter = entry.getKey();
            book = (Book) entry.getValue();
            System.out.println(counter + ". " + book.getBookName());
        }
    }