Java Lab

Task #3 Writing Output to a File

1) Create a new project in NetBeans named StatsDemo. Copy files StatsDemo.java and Numbers.txt into your project. Compile and run.

2) Program doesnt do much but should compile and run with no errors. If not, make sure to fix any errors before moving to next step.

3) First we will write output to a file:

-Create a FileWriter object passing it the filename Results.txt (Dont forget the needed import statement). See page 236 of textbook

-Create a PrintWriter object passing it the FileWriter object.

-Since you are using a FileWriter object, add a throws clause to the main method header.

4) Print the mean and standard deviation to the output file using a three decimal format, labeling each.

5) Close the output file.

6) 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.

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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

}

}

Java Lab Task #3 Writing Output to a File 1) Create a new project in NetBeans named StatsDemo. Copy files StatsDemo.java and Numbers.txt into your project. Compile and run 2) Program doesn't do much but should compile and run with no errors. If not, make sure to fix any errors before moving to next step. 3) First we will write output to a file: -Create a FileWriter object passing it the filename Results.txt (Don't forget the needed import statement). See page 236 of textbook -Create a PrintWriter object passing it the FileWriter object. Since you are using a FileWriter object, add a throws clause to the main method header. 4) Print the mean and standard deviation to the output file using a three decimal format, labeling each. 5) Close the output file. 6) 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