MSc in Computer Science
SE510


Exercise 1: Getting started with Java programming
The purpose of this exercise is to give you the first taste of writing programs using the Java 
Development Kit (JDK).  You will see how to write a program, compile it, and run it, i.e. everything 
that programming really amounts to.
The exercise has been organised as a progressing series of problems.  You are provided with 
explanatory solutions to the first few of them, but the remaining problems, as well as everything in the 
future exercises, will be left for you to tackle.  If you are stuck at any point don’t be afraid to ask for 
help, but before you do that, please make sure you have exhausted all possibilities.

Problem 1. Set up your default login
Edit the file .login in your home directory to include the line:
source /bham/global/Java11Login
after the line
#source /bham/global/EmacsLogin
Do this by:
1. Open a text editor, e.g. xemacs, by typing the following command in the command line 
window:
 > xemacs &
2. Open the file by selecting Open File from the Files menu and enter .login at the bottom of the 
emacs window (~/.login).
3. Save the file (select Save Buffer from the Files menu).
4. Exit xemacs
Problem 2. Create and run a program that prints “Hello 
World”
Solution:
1. Create program source file
1. Open a text editor, e.g. xemacs, by typing the following command in the command line 
window:
 > xemacs &
2. In the editor type the following program into the file or simply copy it from a pretyped one.  In 
order to do that choose Insert File from the Files menu and enter this line at the bottom of the 
emacs window (remember to delete any default characters that xemacs will put there for you).
 /home/pg/mcc/projects/java/HelloWorld.java
 
 class HelloWorld
 {
 	public static void main(String[] arguments)
 	{
 		System.out.println("Hello World!");
 	}
 }
3. When you have created your program file, you need to save it to your directory.  You should 
have a separate directory for your Java programs, so that they are not confused with other files 
that you will create in the future.  To create such a directory, in the command line window 
enter, e.g. the following:
> mkdir java
 Java is an example name.  If you wish to call your directory any other name (e.g. programs, 
projects, or workshop), feel free to do so.
 Now you can save your program into the directory you have just created.  From the Files menu 
choose Save Buffer, and enter the name of the directory followed by a slash sign “/” and the 
name of the file.  The file name has to be the same as the name of the main class of your 
program, i.e. “HelloWorld”, with the suffix “.java”.  It is important that the case of the letters 
in the file name is exactly the same as in the class name.  Therefore, what you enter will look 
something like this:
~/java/HelloWorld.java
where “~” is an abbreviation representing your home directory.
2. Compile the source file
In the command line window, move to your java program directory in order to have direct access 
to your HelloWorld program file.  Use the following command:
> cd java
or any other directory name you have chosen in step 2.1.3.  Now run the Java compiler on 
HelloWorld program file in order to produce code which is understandable to the computer:
> javac HelloWorld.java
If no errors come up, a file called “HelloWorld.class” should appear in the directory where 
“HelloWorld.java” is.  You can check it by entering the command:
> ls
which lists the contents of the current directory.
3. Run the compiled program
In the command line window enter the command:
> java HelloWorld
The program should respond by printing “Hello World!” in the line below the command.
Problem 3. Change the program to display your name 
instead of “World”
Solution:
Come back to the editor window, which should still contain your source program file.  In the line
System.out.println("Hello World!");
replace “World” with your name.  Then save the file by choosing Save Buffer from the Files 
menu, and carry out steps 2.2 and 2.3 again.
Problem 4. Change the program to display your name 10 
times in separate lines
Solution:
Again in the editor, before the line
System.out.println("Hello John!");
insert a new line containing the following loop statement
for (int i = 0; i < 10; i++)
Indent the “System.out... etc.” line by a few space characters, to emphasise that it is nested within 
a loop.  Save the file and then compile and run it.
Problem 5. Change the program to display your name 10 
times, but this time each line should be indented as shown 
below
Hello John!
 Hello John!
  ...
   Hello John!
Solution:
Expand the statement within the loop into a block which includes printing extra spaces in front of 
every new line.  There should be i spaces in front of the i’th line.  We can generate them by using 
another loop that iterates from 0 to i, where i is the number of the current line, produced be the 
main loop.
The following two lines do the job:
for (int j = 0; j < i; j++)
	System.out.print(‘ ‘);
They need to be inserted before the “System.out... etc.” line in your program, but keep in mind 
that, since now we are executing more than one statement in the main loop, we must embrace 
them with a pair of curly brackets, as shown in the skeleton code below:
for (...)
{
	statement1
	...
	statementn
}
Compile the code and see if it works.
Problem 6. Change the program so that it asks for a name 
and the number of times it is to be displayed
Solution:
At the beginning of the file, insert the following line
import java.io.*;
This will import a useful input/output package that we are going to use.  Next, before the main 
loop statement, insert a line that prompts the user for a name, e.g.
System.out.print(“Please enter your name: “);
Declare a string variable that will store the name entered by the user (put this line at the start of 
the function)
String name;
and create an input reader that will bring this name into your program
BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
Now insert a statement that will extract the name from the reader, and place it in the “name” 
variable.
str = reader.readLine();
Next, insert similar code to get the number of iterations from the user
System.out.print(“Please enter number of iterations: “);
int number = Integer.parseInt(reader.readLine());
Note, that we have reused the input reader from above and initialised the number variable with the 
data read from the input.  However, we had to convert the string extracted from the reader into an 
integer number, using the Integer.parseInt() method.
In order for the user data to have effect we have to use the “name” and “number” variables instead 
of the constant values in our program. To do that, replace “10” in the statement
for (int i = 0; i < 10; i++)
 with “number”, and change the line
System.out.println("Hello John!");
to
System.out.println("Hello " + name + ‘!‘);
Try compiling and running the program.  If you have problems, compare it with the original 
version at
/home/pg/mcc/projects/java/HelloWorld1.java
You can view it by selecting Open File from the Files menu and entering the above path.
Problem 7. Check if the following program is correct.  If 
not, correct the mistakes and run it.
class Count
{
	public static void main(String[] arguments)
	{
		while (System.in.read() != ‘\n‘)
			count++;
		System.out.println("Input has " + count + " characters.")
	}
}
Solution: over to you
Problem 8. Write a program called Diamond that generates 
the following pattern
  *
 ***
*****
 ***
  *
Solution: over to you
Hint: see next problem
Problem 9. Explore the course web pages at 
http://www/~rjh/courses/msc/.  Find a hint to solving the 
previous problem
Run Netscape by entering the command:
> netscape &
Problem 10. Print the program written in 8 and its output 
on a printer.
Send the program file to printer lw1 using the command
> lpr -Plw1 Diamond.java
In order to print the output of your program, direct it to a file, like this
> java Diamond > anyfile.txt
Then send it to the printer as before
> lpr -Plw1 anyfile.txt
Problem 11. Email the program generated in 8 to another 
student
In Netscape choose New Mail Message from the File menu.  In the Message Composition 
window enter the recipient’s address, and copy your program into the message body (you can use 
Cut & Paste).  Alternatively, include your program file as an attachment.
Problem 12. Post a message to the cs.courses.msc 
newsgroup introducing yourself
In Netscape choose Open Location from the File menu and enter cs.courses.msc.  In the news 
window that will appear choose New Message from the File menu.  In the Compose window type 
in your message.
Problem 13. Show your work to one of the lab. supervisors
Get one of the lab. supervisors to look at what you have done. They may suggest some changes or 
extensions.

  I walk them through file creation process to give them an idea of program writing. BTW, 
will they know UNIX commands from elsewhere, and what text editor shall we use? I assumed 
emacs for the time being.
  What about source’ing Java11Login?
  What do you think of the idea? You mentioned you would have something to suggest to 
them.