NaiveTicket

The second Objects lab, from the BlueJ book's second chapter.

First you need to FORK this repo into your account, then you need to CLONE that foreked repo, the one in your account. When you are finished with your code, be sure to ADD/COMMIT and PUSH your code to your repo.

Use the URL from your repo as the submission to the portal.

Look for the Chapter 2 file you need in the doc folder. There is 35 pages of reading and exercises in the chapter.

Work through all these exercises. You edit this file with your answers for these exercises.

Exercise 2.1

• Create a TicketMachine object on the object bench.
• Upon viewing its methods, getBalance, getPrice, insertMoney, printTicket.
• Use getPrice method to view the value of the price of the tickets that was set when this object was created.
• Use insertMoney method to simulate inserting an amount of money into the machine.
• Use getBalance to check that the machine has a record of the amount inserted.
  • You can insert several separate amounts of money into the machine, just like you might insert multiple coins or notes into a real machine. Try inserting the exact amount required for a ticket. As this is a simple machine, a ticket will not be issued automatically, so once you have inserted enough money, call the printTicket method. A facsimile ticket should be printed in the BlueJ terminal window.

Exercise 2.2

• What value is returned if you check the machine’s balance after it has printed a ticket?
  • After the ticket is printed, the machine's balance returns to 0.

Exercise 2.3

• Experiment with inserting different amounts of money before printing tickets.
  • Do you notice anything strange about the machine’s behavior?
    • The balance continues to increase
  • What happens if you insert too much money into the machine – do you receive any refund?
    • Inserting excess money and printing a ticket results in the output showing the ticket price along with the total of the excess money. No refund appears to be received.
  • What happens if you do not insert enough and then try to print a ticket?
    • The printTicket() method appears to continue adding the inserted money amounts, even though the balance returns to 0.

Exercise 2.4

• Try to obtain a good understanding of a ticket machine’s behavior by interacting with it on the object bench before we start looking at how the TicketMachine class is implemented in the next section.

Exercise 2.5

• Create another ticket machine for tickets of a different price.
  • Buy a ticket from that machine.
  • Does the printed ticket look different?
    • The printed ticket does not look different, aside from the different price entered.

Exercise 2.6

• Write out what you think the outer wrappers of the Student and LabClass classes might look like – do not worry about the inner part.

   
   public class LabClass { }```
  
  

Exercise 2.7

Does it matter whether we write
public class TicketMachine
or
class public TicketMachine
in the outer wrapper of a class?

• Edit the source of the TicketMachine class to make the change and then close the editor window.
  • Do you notice a change in the class diagram?
    • Yes, the class diagram shows a lattice pattern of red lines.
  • What error message do you get when you now press the compile button?
    • The error message shows <identifier expected>.
  • Do you think this message clearly explains what is wrong?
    • I do not think this message clearly explains what is wrong.

Exercise 2.8

• Check whether or not it is possible to leave out the word public from the outer wrapper of the TicketMachine class.
  • It is possible to leave out the word public from the outer wrapper of the TicketMachine class. The IDE shows the Class compiled with no syntax errors.

Exercise 2.9

• From your earlier experimentation with the ticket machine objects within BlueJ you can probably remember the names of some of the methods – printTicket, for instance.

  • Look at the class definition in Code 2.1 and use this knowledge, along with the additional information about ordering we have given you, to try to make a list of the names of the fields, constructors, and methods in the TicketMachine class.
  • Hint: There is only one constructor in the class.

  • Fields:

    price balance total ticketNumber

  • Constructor:

    TicketMachine

  • Methods:

    getPrice getTicketNumber getBalance insertMoney calculateTotal incrementTicketNumber printTicket

Exercise 2.10

• Do you notice any features of the constructor that make it significantly different from the other methods of the class?
  • The constructor takes in an integer (ticketCost), but does not return any value.

Exercise 2.11

• What do you think is the type of each of the following fields?

private int count;
private Student representative;
private Server host;

• The types of the fields are int, Student, and Server.

Exercise 2.12

• What are the names of the following fields?

private boolean alive;
private Person tutor;
private Game game;

• The names of the fields are alive, tutor, and game.

Exercise 2.13

In the following field declaration from the TicketMachine class

private int price;

does it matter which order the three words appear in?

• Edit the TicketMachine class to try different orderings. After each change, close the editor.

  • Does the appearance of the class diagram after each change give you a clue as to whether or not other orderings are possible?
  • The class diagram changes to show the lattice diagram with red lines. Other orderings of the field declaration do not appear possible.
  • Check by pressing the compile button to see if there is an error message.
  • Make sure that you reinstantiate the original version after your experiments!

Exercise 2.14

• Is it always necessary to have a semicolon at the end of a field declaration?
• Once again, experiment via the editor.
• The rule you will learn here is an important one, so be sure to remember it.
  • A semicolon is necessary at the end of a field declaration. After compiling without the semicolon (at the end of field price, the error ';' expected is shown.)

Exercise 2.15

• Write in full the declaration for a field of type int whose name is status.

  private int status;

Exercise 2.16

• To what class does the following constructor belong?

public Student(String name)

- `public class Student`

Exercise 2.17

• How many parameters does the following constructor have and what are their types?

public Book(String title, double price)

- The Book constructor has 2 parameters and their types are String and double.

Exercise 2.18

• Can you guess what types some of the Book class’s fields might be?

  • String, double, int

• Can you assume anything about the names of its fields?

  • Each Book has a unique title and an associated price.

READ upto and INCLUDING section 2.15 of this chapter.