BookTester

public class BookTester {

    public static void main(String[] args) {

        Book book1 = new Book("Harry Potter and the Goblet of Fire", "J.K. Rowling","1234568901",
                650,35,24.95);
        DigitalBook db1 = new DigitalBook("The Fellowship of the Ring", "J.R.R. Tolkien",
                "9090909090", "PDF",425,40,19.95);

        System.out.println(book1.toString());

        System.out.println(db1.toString());
        System.out.printf("Format of %s: %s\n", db1.getTitle(), db1.getFormat());

    }
}