public class Book {
    String isbn;
    String authors;
    String title;

    public Book(String isbn, String authors, String title) {
        this.isbn = isbn;
        this.authors = authors;
        this.title = title;
    }

    @Override
    public boolean equals(Object o) {
        if (o instanceof Book) {
            Book b = (Book) o;
            return isbn.equals(b.isbn);
        }
        return false;
    }

    @Override
    public int hashCode() {
        return isbn.hashCode();
    }
}