Software and Programming: Lab 1
Exercises (Part 1)
WELCOME TO THE FIRST LAB for Software and Programming. In this lab, you will write,
compile, and run your Java programs.
If Java programming is of an issue for you, then we encourage you to work on the labs
with a partner, but we do not require you to do this. It's a good idea to have someone to
talk to as you work on the lab.
At the end of the lab, you'll find a set of exercises. In general, you should not expect to finish all
the exercises during the lab. Finishing the exercises is homework. In particular, we expect you to
clean up any programs you write and take the time to give thoughtful answers to essay
questions.
Outline of the Lab:
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
Your Computer Accounts
Your First Java Programs
Exercises
Your Computer Accounts
In the world of networked computers, you can sit at one computer and access computers from
across campus and around the world. As a student at Birkbeck College, you have an account on
the College computers. Having an account means that you have a user name and password that
you can use to log on to the computer. You also have a directory on each computer where you
can store files (which are stored centrally). You can also access files stored in other directories
on the computers. Your username on each of these computers is the same.
The main programs you should use for this course is JDK (Java Developers Kit) and BlueJ (an
introduction of how to use BlueJ is given in part 2 of this lab sheet). Note: the following website
gives
a
description
of
how
to
setup
Java
on
your
own
computer
http://www.ics.uci.edu/~thornton/ics22/LabManual/SettingUpJava.html.
For more information on using your account, you should read the Web pages at
http://www.bbk.ac.uk/ccs. In this lab, you will need to know a few commands for working
with files and directories. You should know at least the concepts of file, directory, path
name, and home directory.
Your First Java Programs
In these exercises, you will use the “TicketMachine” example and work with it to modify
and improve it. You will also build Java programs from scratch.
Exercise 1:
NOTE: You can either use BlueJ to do the “HelloWorld” exercise below or use an
editor such as Textpad, Notepad (if you choose this option, you need to type
commands in the DOS console). If you decide to use BlueJ and are unfamiliar with
this software, part 2 of this lab explains how to use BlueJ.
You should type in the HelloWorld program (see Figure 1) into a file HelloWorld.java, which simply
prints out the message "Hello World". To run the program you must first compile HelloWorld.java. If
If you are using an editor, do this with the command
javac HelloWorld.java
After doing this, the compiler has created a file named HelloWorld.class. This is the compiled, Java
bytecode version of the HelloWorld program. Now that the compiled program exists, you don't
have to compile the program ever again, unless you want to edit it and change what it does. If
you are using an editor, run the program with the command:
java HelloWorld
The computer will say hello to the world. (Note that you say "java HelloWorld" to execute the
class file, and not "java HelloWorld.class".)
public class HelloWorld {
public static void main(String[] args) {
System.out.println("Hello World!");
}
}
Figure 1: HelloWorld program
Exercise 2:
Before attempting the rest of the exercises in part 1 of lab 1, switch over to part 2 of the lab
sheet and come back to this section once you have completed part 2. From now on, we
recommend you use BlueJ.
Exercise 3:
Exploring the behavior of a naïve ticket machine
Open the naive-ticket-machine project (http://www.dcs.bbk.ac.uk/~gngch01/sandp1) in BlueJ.
When you create a TicketMachine instance, you will be asked to supply a number that
corresponds to the price of tickets that will be issued by that particular machine. The price is
taken to be a number of cents, so a positive whole number such as 500 would be appropriate
as a value to work with.
3-1 Create a TicketMachine object on the object bench and take a look at its methods. You
should see the following: getBalance, getPrice, insertMoney, and printTicket. Try out the
getPrice method. You should see a return value containing the price of the tickets that was set
when this object was created. Use the insertMoney method to simulate inserting an amount of
money into the machine and then 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.
3-2 Experiment with inserting different amounts of money before printing tickets. Do you notice
anything strange about the machine’s behavior? What happens if you insert too much money
into the machine – do you receive any refund? What happens if you do not insert enough and
then try to print a ticket?
3-3 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.
Exercise 4:
For your next exercise, you will write a program that does a computation and prints out a
result.
Here are some facts: Every year, 724 billion cubic yards of water flow out of the
Mississippi. There are 1760 yards in a mile. There are 365 days in a year. Here is the
question: How many cubic miles of water flow out of the Mississippi every day? Some
Java commands that will get the job done are:
double cubicYardsPerYear = 724000000000.0;
double cubicYardsPerDay = cubicYardsPerYear / 365;
double cubicMilesPerDay = cubicYardsPerDay / (1760*1760*1760);
System.out.println("The answer is " + cubicMilesPerDay);
For a complete program, you have to put this inside the standard Java program wrapper:
public class Mississippi {
public static void main(String[] args) {
double cubicYardsPerYear = 724000000000.0;
double cubicYardsPerDay = cubicYardsPerYear / 365;
double cubicMilesPerDay = cubicYardsPerDay / (1760*1760*1760);
System.out.println("The answer is " + cubicMilesPerDay);
}
}
This should be in a file called Mississippi.java.