Using MsgBox3.java or Average.java as examples, create a Java non-GUI stand-alone application that displays a histogram. A histogram is a kind of non-GUI bar chart (see example bar chart) that shows how many times a given value occurs in an input sample. The more times a given value appears, the longer the bar becomes for that value. With a histogram, you draw the chart sideways.
This program can be used to examine all sorts of frequency data.
In the example below, I used this histogram
program to analyze the scores of a previous COP 2800 Exam #1.
I entered in all the question numbers that
were answered incorrectly, for each and every student exam.
(For instance, on the first student answered questions
1, 3, 4, and 19 incorrectly, so I input:
1 3 4 19.
The next student had questions 4, 17, 19, and 22 incorrect, so I continued
4 17 19 22 this time.
I kept this up for each student's exam.)
shows 8 questions were much harder than the rest,
and that two questions were so trivial nobody answered them
(I have used this information to update my test bank.)
To actually draw the horizontal lines of the histogram, you
must use the
you created in TextKit Project.
If you don't have a working
utils package, I can supply one,
but not using your original one will cost you some credit.
This project will require the use of arrays and input.
Write a Java non-GUI program that will accept as
input integer values from the standard input,
each value is a number between 1 and 25.
The input might contain any number of values separated by white-space.
The user will indicate the end of the list by signaling
EOF, which on Windows systems is done by hitting
(On Unix and Macintosh systems EOF
can be signaled by hitting
The output shall consist of 25 lines of stars (asterisks),
one line for each of the possible input values (the numbers
The number of stars drawn shows how many times each value
was entered as input.
Each line should be labeled with the value it is showing the bar
So, if the input was:
C:\TEMP> java Histogram Enter integers <= 25, one per line, hit control-Z when done: 1 2 4 2 1 2 control-Z
Then the output would be:
1: ** 2: *** 3: 4: * 5: 6: 7: 8: 9: 10: 11: 12: 13: 14: 15: 16: 17: 18: 19: 20: 21: 22: 23: 24: 25:
Your Java program must use the method
lineOfStars to create the stars for each line
This method must take a single
int parameter which says how many stars to draw.
This method must be a
method of a class called
which must be in a
This should be the method you created for the previous project.
You are not allowed to modify your
utils.TextKit class in any way from what you completed
in the previous project without the approval of your instructor.
Your program will have its class in the default, nameless package, or any
other packege you want to create, except in the
TextKit is located).
(Note only a few of the more than 100 values actually typed by me are shown here.)
C:\TEMP> java Histogram Enter integers <= 25, one per line, hit control-Z when done: 1 5 16 11 2 23 3 2 ... 16 control-Z Histogram showing how many students answered each question wrong: 1: ** 2: ***** 3: ***** 4: 5: *** 6: ** 7: ***** 8: 9: ** 10: *************** 11: ***** 12: ******** 13: ************* 14: ******** 15: ******* 16: *************** 17: *** 18: ************** 19: ******************* 20: ********** 21: ******* 22: ******** 23: ************* 24: ************** 25: **************** C:\TEMP>
Make sure you understand the histogram: each entered value is represented
by one star, so the total number of stars equals the number of input values.
The length of each line of stars represents the number of times that input
value was entered.
For example, for the input value of
17, you can see three stars,
which means that number was input three times.
Start this project by creating a skeleton class with a stub
Then think about what the program should do, and add comments for that.
You should be asking yourself “does the program need to store the
input?” and “what kind of loop(s) should be
Don't start writing any code until you understand what your code should do.
Many students make the mistake of thinking the input data is the length of each bar. Take another look at the sample data and the resulting output. The input is not the lengths of the 25 bars!
It may help to think of the input as a series of “bar numbers” instead. For the first part of your program you must read these numbers one at a time, and increment a counter, (that stores that bar's length), for each one. You repeat this until you run out of input data. The second part of your program needs to print each of the 25 bars.
Java 5 provides input methods (the
that make reading the input (and converting to Integers) very easy.
You are encouraged to use them.
Any program that reads input from standard input can read input data from a file too. This technique is known as input redirection and is very useful when testing. To read data from a file instead of the keyboard, run your program using a command line such as:
C:\TEMP> java Histogram < data.txt
To practice using the same data I used, download HistogramData.txt and use that as the input, as shown above.
You program should be easily read and well commented, including your name. Remember the best programs result when you start with the design, then make a skeleton class containing your design as comments, and finally fill in the code below each comment, one piece at a time. If you wish you can send me your design “skeleton” program before starting to write any code, to make sure you're on the right track.
Ask me for help if you get stuck!
Email to me a copy of the source code for your Histogram class.
You do not need to send your
.class files nor your
Send projects to
Please use a subject such as "Java Histogram Project"
so I can tell which emails are submitted projects.
Send project questions to . Please use a subject such as "Java Histogram Project Questions" so I can tell which emails are questions about the project.