Gregorian Calendar Cannot Be Converted Into Double

I wrote this application but somehow in my CheckingAccount, I get an error saying GregorianCalander cannot be converted into double.

The line that gives me an error is "super(name, number, openDate, balance);"

package finalproject;
import java.util.*;
import java.text.SimpleDateFormat;
public class CheckingAccount extends Account {
final SimpleDateFormat sd = new SimpleDateFormat("yyy/mm/dd");
CheckingAccount(String name, String number, GregorianCalendar openDate, double balance) {
super(name, number, openDate, balance);

[Code] .....