Java Lab

Task #5 Calculating the Standard Deviation

1) We need to reconnect to the file so we can start reading from the top again.

-Create a File object passing it the filename.

-Create a Scanner object passing it the File object.

2) Reinitialize the sum and count to 0.

3) Write a priming read to read the first line of the file.

4) Write a loop that continues until you are at the end of the file.

5) The body of the loop will:

-convert the line into a double value and subtract the mean, store the result in difference

-add the square of the difference to the accumulator

-increment the counter

-read a newline from the file.

6) When the program exits the loop, close the input file.

7) The variance is calculated by dividing the accumulator (sum of the squares of the difference) by the counter. Calculate the standard deviation by taking the square root of the variance (Use the Math.sqrt method to take the square root).

8) Compile, debug, and run. You should get a mean of 77.444 and standarddeviation of 10.021.

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Code Listing 4.2 (StatsDemo.java)

import java.util.Scanner;

// TASK #3 Add the file I/O import statement here

/**

This class reads numbers from a file, calculates the mean and standard deviation, and writes the results to a file.

*/

public class StatsDemo

{

// TASK #3 Add the throws clause public static void main

(String[] args)

{

double sum = 0; // The sum of the numbers

int count = 0; // The number of numbers added

double mean = 0; // The average of the numbers

double stdDev = 0; // The standard deviation

String line; // To hold a line from the file

double difference; // The value and mean difference

// Create an object of type Scanner

Scanner keyboard = new Scanner (System.in);

String filename; // The user input file name

// Prompt the user and read in the file name

System.out.println("This program calculates " +

"statistics on a file " + "containing a series of numbers"); System.out.print("Enter the file name: ");

filename =

keyboard.nextLine();

// ADD LINES FOR TASK #4 HERE

// Create a File object passing it the filename

// Create a Scanner object passing File object

// Perform a priming read to read the first line

//of the file

// Loop until you are at the end of the file

// Convert the line to a double value and add the

// value to sum

// Increment the counter

// Read a new line from the file

// Close the input file

// Store the calculated mean

// ADD LINES FOR TASK #5 HERE

// Reconnect File object passing it the

// filename

// Reconnect Scanner object passing

// File object

// Reinitialize the sum of the numbers

// Reinitialize the number of numbers added

// Perform a priming read to read the first line of

// the file

// Loop until you are at the end of the file

// Convert the line into a double value and

// subtract the mean

// Add the square of the difference to the sum

// Increment the counter

// Read a new line from the file

// Close the input file

// Store the calculated standard deviation

// ADD LINES FOR TASK #3 HERE

// Create a FileWriter object using "Results.txt"

// Create a PrintWriter object passing the// FileWriter object

// Print the results to the output file

// Close the output file

}

}