DescriptionSpecification
Learning Objectives
By completing this assignment, students will be able to:
•
Implement a well-designed Java class to meet a given specification
•
Use arrays to
•
o
Explore datasets and make informed conclusions
o
Create and manipulate visualizations
Follow prescribed conventions for code quality, documentation, and readability
Program Behavior
You can see an example interaction with the program below (user input is bold and
underlined):
This interaction produces a disneyland_stats.txt file that looks like this:
And also produces a world_cup_stats.txt file that looks like this:
The program begins by printing a short introduction and prompting the user for an
input file containing a dataset (see below for the expected dataset format). It also
prompts the user for an output file. The program will then process the dataset and
generate a text-based histogram. It will also compute and print some summary
statistics of the data: the number of values read, the mean (average), and the mode
(most common value). The program prints the histogram and summary statistics to the
output file specified by the user. It then repeatedly prompts the user for an input and
output file name until the user enters anything other than “yes” (case-insensitive)
to “Do you want to create another histogram?”.
You may assume the user will enter a valid input file name (i.e., an existing file) as well
as a valid output file name (any file name ending with .txt).
Dataset Format
Each input file for this program will include a single dataset, with one number per line.
The first value in the file will be the total number of values in the dataset. The value will
then be followed by each individual data point, one per line. You may assume that all
values in each dataset are integers, that all values are non-negative (i.e., greater than or
equal to zero), and that the dataset is not empty (contains at least one value).
We have provided several sample datasets for you to work with.
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seattle_temps.txt – Average daily temperatures in Seattle for the year 2021,
retrieved from the National Oceanic and Atmospheric Administration.
•
disneyland.txt – Ratings on Trip Advisor for Disneyland California from April
2019, retrieved from Kaggle.
•
world_cup.txt – Total goals per game from the 2018 FIFA World Cup, retrieved
from https://gitlab.com/djh_or/2018-world-cupstats/blob/master/world_cup_2018_stats.csv.
You may assume that the user will enter a valid file name. If you would like, you can
also provide your own data! If you choose to analyze your own dataset, be sure it also
meets the above requirements.
Histogram Format
The histogram output by your program should begin at 0 and end at the largest value
in your dataset. Each line of the histogram should represent one value and should
consist of the value followed by a vertical bar (‘|’), a space, and then one asterisk (‘*’)
for each occurrence of that value in the dataset. All values between 0 and the
maximum value in the dataset should be represented– if a value does not occur in the
dataset, your program should still print a line for that value but print zero asterisks on
that line.
Program Structure
Your program should utilize methods, parameters, and returns to add a clear and
understandable structure to the code. In particular, your code should include at least
the following 7 methods with the indicated parameters and return values:
1. A method to print the program’s introduction message
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no parameters
o
no return value
2. A method to read in the data from an input file
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takes one parameter, a Scanner
o
returns an array containing the data read from the parameter Scanner
3. A method to find the index of the maximum value in an array
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takes one parameter, an array of integers
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returns the index at which the maximum value of the array occurs
▪
If the maximum value occurs multiple times, return the index of
the first occurrence
4. A method to count the occurrences of each value in an array
o
takes one parameter, an array of integers
o
returns an array containing the number of times each value occurs in the
parameter array
5. A method to compute the mean (average) of the data in an array
o
takes one parameter, an array of integers
o
returns the mean (average) of the data in the parameter array
6. A method to print a text-based histogram
o
takes two parameters: an array of integers, and a PrintStream object
o
no return value
7. A method to compute and print the summary statistics
o
takes three parameters: an array of integers containing data, an array of
integers containing counts of that data, and a PrintStream object
o
no return value
With the exception of methods 3 and 5, all these methods should be called from main. Method 3
should be called twice, once in method 4 and once in method 7. Method 5 should be called from
method 7.
HINT: The two calls to method 3 should pass different arrays as parameters: one call will pass the data
from the file; the other call will pass the array of counts produced by method 4.
You may include additional methods if you wish, but you must include these methods
as defined. (Naturally, your program will also include a main method.)
Along with the required methods above, you must have a loop in main which allows
the program to keep creating histograms until the user chooses to stop.
Finally, your program must only read the input and output file once. You may not
reset a Scanner, and you may not create more than one Scanner connected to the input
file. Likewise, you may not create more than one PrintStream connected to the output
file.
findMaxIndex & getCounts Development
Here, you will implement two of the seven required methods for your program:
findMaxIndex (method 3) and getCounts (method 4). Since other aspects of your
program will rely on the correctness of these two methods, we provide several tests for
them on this slide. Make sure you pass all tests here, and then you should use these
two methods in your program on the next slide!
1️⃣ findMaxIndex
First, implement the findMaxIndex method. This method should find the index of the
maximum value in an array of integers. It should also:
•
take one parameter, an array of integers
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return the index at which the maximum value of the array occurs
o
If the maximum value occurs multiple times, return the index of the first
occurrence
Press Mark to test your method. If you’ve implemented it correctly, you should pass all
findMaxIndex test cases!
2️⃣ getCounts
Once you get findMaxIndex working, implement the getCounts method. This method
should count the occurrences of each value in an array of integers. It should also:
•
take one parameter, an array of integers
•
return an array containing the number of times each value occurs in the
parameter array
To help you get started, here is a visual representation of creating a counts
(occurrences) array:
Each index number of the counts array represents a data value. Since the largest
data value in the data array is 3, the highest index of the counts array must be 3, which
means the size of the counts array must be 4.
Completed code below:
import java.util.*;
public class Development {
public static void main(String[] args) {
int[] diagramData = {1, 2, 1, 1, 3, 2};
System.out.println(“max index of diagramData = ” +
findMaxIndex(diagramData));
System.out.println(“counts array for diagramData = ” +
Arrays.toString(getCounts(diagramData)));
int[] exampleData = {1, 0, 1, 5, 4, 4, 2, 3, 5, 1};
System.out.println(“max index of exampleData = ” +
findMaxIndex(exampleData));
System.out.println(“counts array for exampleData = ” +
Arrays.toString(getCounts(exampleData)));
}
public static int findMaxIndex(int[] data) {
int maxIndex = 0;
for(int i = 1; i < data.length; i++) {
if (data[i] > data[maxIndex]) {
maxIndex = i;
}
}
return data[maxIndex];
}
public static int[] getCounts(int[] data) {
int maxValue = 0;
for (int i = 0; i < data.length; i++) {
if (data[i] > maxValue) {
maxValue = data[i];
}
}
int[] counts = new int[maxValue + 1];
for (int i = 0; i < data.length; i++) {
int value = data[i];
counts[value]++;
}
return counts;
}
}
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