Task #1 Writing Output to a File 1. Copy the files StatsDemo.java (see Code Listing 4.2) and Numbers.txt from the Student Files or as directed by your instructor. 2. First we will write output to a file: a. Create a File object passing it the filename Results.txt (Dont forget the needed import statement). b. Create a PrintWriter object passing it the File object. c. Since you are using a File object, add a throws clause to the main method header. d. Print the mean and standard deviation to the output file using a three-decimal format, labeling each. e. Close the output file. 3. Compile, debug, and run. You will need to type in the filename Numbers.txt. You should get no output to the console, but running the program will create a file called Results.txt with your output. The output you should get at this point is: mean = 0.000, standard deviation = 0.000. This is not the correct mean or standard deviation for the data, but we will fix this in the next tasks.

Task #2 Calculating the Mean 1. Now we need to add lines to allow us to read from the input file and calculate the mean. a. Create a File object passing it the filename. b. Create a Scanner object passing it the File object. 2. Write a priming read to read the first line of the file. 3. Write a loop that continues until you are at the end of the file. 4. The body of the loop will: a. convert the line into a double value and add the value to the accumulator b. increment the counter c. read a new line from the file 5. When the program exits the loop close the input file. 6. Calculate and store the mean. The mean is calculated by dividing the accumulator by the counter. 7. Compile, debug, and run. You should now get a mean of 77.444, but the standard deviation will still be 0.000.

Task #3 Calculating the Standard Deviation 1. We need to reconnect to the file so we can start reading from the top again. a. Create a File object passing it the filename. b. 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: a. convert the line into a double value and subtract the mean, store the result in difference b. add the square of the difference to the accumulator c. increment the counter d. 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 standard deviation of 10.021.

import java.util.Scanner;

// TASK #1 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 #1 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();

//------------------------------------------------------------ TASK 2

// ADD LINES FOR TASK #2 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

// Add value to sum

// Increment the counter

// Read a new line from the file

// Close the input file

// Store the calculated mean

//------------------------------------------------------------ TASK 3

// ADD LINES FOR TASK #3 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

// 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

//------------------------------------------------------------ TASK 1

// ADD LINES FOR TASK #1 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

}