Firebase

FirebaseUtil.java

public class FirebaseUtil {

    public static void saveData(){

        List<Author> authorList = new ArrayList<>();
        Author author1 = new Author("Robert C. Martin");
        authorList.add(author1);
        Book book = new Book("Clean Code", authorList);
        DatabaseReference database = FirebaseDatabase.getInstance().getReference();
        DatabaseReference databaseBook = database.child("book");
        databaseBook.push().setValue(book);

    }

}