The goal to actually write your first Java programs, then compile and run them. In particular, you will practice some basic operations on Strings, in addition to continuing to practice some of the algorithmic thinking we had previously been doing.
Starting this week, you will be doing labs in pairs, using special lab accounts. So you'll need to find a partner for this week (or possibly a third, if the number of students in lab today is odd). There will be instructions at the end of the lab about how you can copy your work to your own account.
Make a new directory for this lab and cd into it.
mkdir lab2 cd lab2
I am providing stubs for the programs you are going to write. Copy them from the course public directory. (Don't miss the dot as the second argument.)
cp /cslab/class/csci235/lab2/* .
Look at the list of files now in your directory.
ls
You should see Greeting.java
,
StringToInt.java
,
and Palindrome.java
.
This first exercise is just to step you through
the process of writing, compiling, and running a
Java program.
Open Greeting.java
in XEmacs.
xemacs Greeting.java &
Remember that the ampersand means that the terminal window will still be active even though XEmacs is running.
Add your names to the @author
tag.
Then add a line to the program (inside the main
section) that displays a greeting to the screen.
Then compile the program.
javac Greeting.java
If the compiler complains, then look carefully at your program (you probably wrote only one line, so it should be easy to fine the problem) and see if you can figure out what's wrong and try again. If the compiler does not give you any errors, then congratulations, you have compiled your first program. Look at the contents of the directory again.
ls
You should see Greeting.class
.
If you want to see only the source files, you can type
ls *.java
This means, "list everything that ends with '.java
'."
Now run the program.
java Greeting
(Remember that when you compile, you compile a file,
so you need to give javac
the name of the file,
Greeting.java
.
When you run, you run a program, and the name
of the program is Greeting
,
not Greeting.class
.
The Java virtual machine knows to look for a file called
Greeting.class
for the compiled version of
the program Greeting
.)
Now that your program runs correctly, give your partner a HIGH FIVE!
This one is going to be a little harder.
Open StringToInt.java
(you can do this in the same XEmacs session by
clicking on the "open" button, or by typing ^X^F
and
filling in the filename).
Your task here is to take a String that the user
inputs and convert it into an int.
I have already written the part that prompts the
user for a string--it requires some stuff we haven't
learned yet, so don't let it intimidate you.
Just know that by the time that stuff is done,
str
will contain a String that the user
of the program has typed in.
Assume the string contains only
digits, such as "142364
".
Your task is to store the equivalent value
in the int variable x
.
Here's one bit of magic that you'll need.
If you have a char value---let's say, the variable
c
---that contains a digit,
then you can turn that digit into the
equivalent int---say, to store in the variable i
---by
i = (int) (c - '0');
Do not change any of the lines of code I have given you (except you may delete the "put your code here" line).
You may assume the the string you are given contains only digits. Your program does not need to work right for incorrect input. (That's only because this is your first crack at programming; in principle, programs should deal with incorrect input gracefully.)
When you compile, you will almost certainly get errors. Don't be afraid to ask for help. When it compiles without errors, then test the program by running it on several inputs. Do not be surprised if it doesn't work right; go back and fix it.
When your program is working, go on to the next problem.
A word, phrase, or sentence is a palindrome if it is the same backwards and forwards. (For phrases and sentences, we ignore punctuation, spaces, and capitalization). Some interesting palindromes are
Open the file Palindrome.java
.
Your task in this problem is to test if
a word entered by the user (stored in the variable
str
) is a palindrome.
For our purposes, we will assume we're working
only on single words.
(Some English words that are palindromes are
level, racecar, and wow).
Print an appropriate message to the screen.
As before, compile and test.
As a general rule, you will be asked to turn in your labs by using a command that bundles up your files and puts them in a grading directory. Sometimes we will ask you to turn in a printed copy of certain files. Today, you'll do both.
The first thing you need to do is prepare a script file that records you compiling and running your files. Here are the steps to take:
.class
) versions of your
files. This time, that will be
rm Greeting.class StringToInt.class Palindrom.class
Everything that goes to your terminal will now also be recorded in the a file named typescript.script
ls -l
javac Greeting.java
This program is so simple that a single run will do.java Greeting
StringToInt.java
and
Palindrome.java
. You should run each of these
programs several times, using different inputs to show that it
works for a representative set of cases.
exit
.
Be sure that you see the report of successful submission./cslab/class/csci235/bin/handin lab2 Greeting.java StringToInt.java Palindrome.java typescript
Before printing a script file, you need to clean it up. To clean up
typescript
use the command
Now print all of this out in a reasonably neat manner, using the command/cslab/class/csci235/bin/cleanscript typescript > typescript.clean
The commanda2ps --file-align=fill Greeting.java StringToInt.java Palindrome.java typescript.clean
a2ps
formats the output nicely,
two-up (with two pages per side) and sends it to
the lab printer. The --file-align=fill
tells a2s to
not start each new file on a new sheet.
Turn in the hard copy to me.
When you come back later, you may not be working on the same account. So
you will probably want to copy what you have done today to
your own account. You can do that using the file browser
without too much difficulty. In the instructions that
follow, the username is msnerd
; substitute yours.
lab2
folder where you have been working.
SSH
cslab25
(or any of the
other cslab machines)
/homes/msnerd
(but with
your username)
When you're done, disconnect your home directory. Your partner will want to do the same thing to copy the files to his/her home, too.