The self-test quiz for this week is here

Task 1: Catch Up

If you haven’t completed exercises from previous labs, you may use this week’s lab to catch up on unfinished work.

If you are up-to-date, you can carry on with the following exercises.

Task 2: Return to the Ticket Machine

Go back to the ticket machine project you worked on in last week’s tut.

1. Create a new class Ticket which represents a ticket.
2. Create appropriate fields. What information should a Ticket carry?
3. Create a constructor to initialise these fields.
4. Now modify purchaseTicket on the TicketMachine class so that it creates a new Ticket object and returns it, rather than printing it.

Let’s suppose now that a ticket has 10 charges. Each time we use it, one charge is lost.

1. Change your Ticket class to track charges. What changes do you need to make to do this?

Now let’s add a recharge method to the TicketMachine. It should take a Ticket as a parameter and reset its charges to 10 but at the cost of 1/10th of the ticketPrice for every charge added (if the user has enough balance). Implement this in stages:

1. Make the method just recharge the Ticket for free.
2. Compute how much the recharge will cost. You will need to use an accessor method on the Ticket to find out how much charge it has.
3. Add a test to see if the user has enough balance.
4. If there is not enough balance print an error message and do not recharge.
5. Subtract the charge from the balance.

Task 3: Clock (if time permits)

Take a look at the clock project from Chapter 3 of the textbook.

1. Investigate the NumberDisplay class first. How does it work?
2. Look at the setValue method. What does the && operator do? This is a boolean operator. Try experimenting with it in the Code Pad.
3. Look at the increment method. What does the % operator do? Try experimenting with it in the BlueJ Code Pad.
4. Now take a look at the ClockDisplay class. Try to understand how it works.
5. ClockDisplay has two constructors. How do they differ?
6. The second constructor does not call updateDisplay. Is this a bug? Why/why not?
7. Change this class to have a seconds field as well as hours and minutes.
8. Change the class to show a 12 hour clock with AM/PM.