Conditions within subclass constructors?

Question

My assignment is to create a Ticket class with three subclasses, WalkupTicket, AdvanceTicket and StudentAdvanceTicket.
AdvanceTicket and StudentAdvanceTicket both must have two parameters, the ticket number, and the number of days in advance the ticket is purchased. Depending on how early the ticket was purchased, the price varies. WalkupTicket is easy since it only has one price, but the other two are giving me a hard time. What I want to do is something like this;
public class Ticket {
     private int number; // Instance variable containing ticket number
     private int price;  // Instance variable containing ticket price
     public Ticket (int n, int p) {
          number = n;
          price = p;
     public static class AdvanceTicket extends Ticket {
          public AdvanceTicket (int n, int d) {
               if (d >= 10) super(n, 30);
               else super(n, 40);
}But that doesn't work because the first line in the subclass constructor must call the superclass constructor.
I've tried creating a checkPrice method within the subclass, then using super(n, checkPrice(d)); but that gives me an error as well, telling me I have to call the super constructor before calling the method.
Can someone point me in the right direction?

Answer 1

While it is possible to achieve by making the field package private/protected/public, that is not a good approach. Fields should be made private unless you have good reason not to. Furthermore doing so won't change anything, you will still be invoking a super constructor; an [implicit call to super();|http://java.sun.com/docs/books/jls/third_edition/html/classes.html#8.8.7] will be inserted for you.
The wording of the assignment is somewhat woolly, but I'm certain the original solution does not violate the requirements.
EDIT: I just realized you are using an inner class. The reason you can't instantiate it is that it needs an instance of Ticket first:
Ticket t = null;
WalkupTicket wt = t.new WalkupTicket(1);So in order to create a ticket you would need a ticket first, that's not useful.. ;)
Using a nested class (making WalkupTicket static again) can be made to work with an explicit upcast:
public abstract class Ticket {
    private int number; // Instance variable containing ticket number
    private int price;  // Instance variable containing ticket price
    // Creates a WalkupTicket
    // @param n is the ticket number
    public static class WalkupTicket extends Ticket {
        public WalkupTicket (int n) {
            ((Ticket)this).number = n;
            ((Ticket)this).price = 50;
}With kind regards
Ben
Edited by: BenSchulz on Feb 13, 2010 12:27 PM