Task #3 Reading and Writing Using Files 1. FileStats.java below, you can compile
ID: 3681269 • Letter: T
Question
Task #3 Reading and Writing Using Files
1. FileStats.java below, you can compile FileStats.java. It
will compile without errors so that you can use it to test out the StatsDemo class you will be creating.
2. Create a class called StatsDemo which consists of a main method to do the following:
a) Create a DecimalFormat object so that we can format our numbers for output with 3 decimal
places (Dont forget the needed import statement).
b) Create a Scanner object to get the file name input from the user (Dont forget the needed import
statement).
c) Prompt the user and read in the file name (Remember to declare any needed variables).
d) Create a FileStats object passing it the file name.
e) Create a PrintWriter object passing it the filename Results.txt (Dont forget the needed import
statement).
f) Since you are using a PrintWriter object, add a throws clause to the main method header.
g) Print the mean and standard deviation to the output file using a three decimal format, labeling
each.
h) Close the output file.
3. Compile, debug, and run. 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 #4 The calculateMean Method
1. Open FileStats.java for editing. You will notice that the calculateMean and calculateStdDev methods do
not do any calculations yet. They simply return a 0 to the constructor to initialize the instance variables.
We need to add lines to each of these methods to have them return the correct value. Lets work with the
calculateMean method first.
2. Create a File object passing it the filename (Dont forget the needed import statement).
3. Create a Scanner object passing it the File object.
4. Since you are using a Scanner object to open a file, add a throws clause to the calculateMean method
header as well as the constructor method header (since it calls the calculateMean method).
5. Declare local variables for an accumulator of type double, a counter of type integer, and line of type
String. Initialize all number variables to 0.
6. Write a loop that reads values from the file until you are at the end of the file.
7. The body of the loop will
a) read a double from the file and add the value to the accumulator
b) increment the counter
8. When the program exits the loop close the input file.
9. Calculate and return the mean instead of 0. The mean is calculated by dividing the accumulator by the
counter.
10. Compile, debug, and run. You should now get a mean of 77.444, but the standard deviation will still
be 0.000.
Task #5 The calculateStdDev Method
1. Do steps 2-6 as above in the calculateMean method but add another local variable called difference of
type double.
2. The body of the loop will
a) read a double value from the file, subtract the mean from that value, and
store the result in difference
b) add the square of the difference to the accumulator
c) increment the counter
3. When the program exits the loop close the input file.
4. 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 Math.sqrt ( ) to
take the square root).
5. Compile, debug, and run. You should get a mean of 77.444 and standard deviation
of 10.021.
-----------------------------------
public class FileStats
{
private double mean; //the arithmetic average
private double stdDev; //the standard deviation
//constructor calls calculateMean and calculateStDev
//methods and store the results in the respective instance variables
public FileStats(String filename)
{
mean = calculateMean(filename);
stdDev = calculateStdDev(filename);
}
//return the mean
//accessor method
public double getMean()
{
return mean;
}
//return the standard deviation
public double getStdDev()
{
return stdDev;
}
//return the calculated arithmetic average
public double calculateMean(String filename)
{
//ADD LINES FOR TASK #4 HERE
//Task #4 the calculatedMean Method
return 0;
}
//return the calculated standard deviation
public double calculateStdDev(String filename)
{
//ADD LINES FOR TASK #5 HERE
//Task #5 the calculateStdDev Method
return 0;
}
--------------------------------------------------------
import java.text.DecimalFormat;
import java.util.Scanner;
import java.io.*;
public class StatsDemo
{
/**
* @param args
*/
public static void main(String[] args)throws IOException //throws clause
{
//create an object of type Decimal Format
DecimalFormat threeDecimals = new DecimalFormat("0.000");
//create an object of type Scanner
Scanner keyboard = new Scanner(System.in);
//declare your variables
String filename; //the user input file name
//prompt the user and read in file name
System.out.println("This program calculates statistic on a file contain a series of number.");
System.out.println("Enter the file name: ");
filename = keyboard.nextLine();
//create the object of type stats using the user input file name
//using the FileStat class
//create an object of the PrintWriter using "Result.txt".
PrintWriter output = new PrintWriter("Result.txt");
//Create a Scanner object passing it the File object.
//print the results to the output file
output.println("mean = " + formatter.format(stats.getMean())
//output for stdDev
//close your output file
output.close();
Explanation / Answer
FileStats.java
// To calculate the statistics on a file of numbers
import java.io.*; // for I/O classes
import java.util.Scanner; // for the Scanner class
public class FileStats
{
private double mean; //the arithmetic average
private double stdDev;//the standard deviation
//Constructor calls calculateMean and calculateStdDev methods
//and store the results in the respective instance variables
public FileStats(String filename) throws IOException
{
mean = calculateMean(filename);
stdDev = calculateStdDev(filename);
}
//returns the mean
public double getMean()
{
return mean;
}
//returns the standard deviation
public double getStdDev()
{
return stdDev;
}
//returns the calculated arithmetic average
public double calculateMean(String filename)throws IOException
{
//Create a File object passing it the filename
File file = new File(filename);
//Create a Scanner object passing it the File object.
Scanner input = new Scanner(file);
double total = 0; //the sum of the numbers
int count = 0; //the number of numbers added
//loop that continues until you are at the end of the file
while (input.hasNext())
{
//convert the line into a double value and add the value to the sum
total += input.nextDouble();
//increment the counter
count++;
}
//close the input file
input.close();
//return the calculated mean
return total/count;
}
//returns the calculated standard deviation
public double calculateStdDev(String filename)throws IOException
{
//Create a File object passing it the filename
File file = new File(filename);
//Create a Scanner object passing it the File object.
Scanner input = new Scanner(file);
double total = 0; //the sum of the numbers
int count = 0; //the number of numbers added
double difference; //difference between the value and the mean
//loop that continues until you are at the end of the file
while (input.hasNext())
{
//convert the line into a double value and subtract the mean
difference = input.nextDouble()- mean;
//add the square of the difference to the sum
total += Math.pow(difference,2);
//increment the counter
count++;
}
//close the input file
input.close();
//return the calculated mean
return Math.sqrt(total/count);
}
}
StatsDemo.java
/**
* StatsDemo class
*/
import java.util.Scanner; //for keyboard input
import java.io.*; //for using files
public class StatsDemo
{
public static void main(String [] args) throws IOException
{
//create an object of type Decimal Format
//create an object of type Scanner
Scanner keyboard = new Scanner (System.in);
String inFilename; // the user input file name
String outFilename;
inFilename = "Numbers.txt";
outFilename = "Results.txt";
//create an object of type Stats using the user input file name
FileStats stats = new FileStats(inFilename);
//create an object of PrintWriter using "Results.txt".
PrintWriter output = new PrintWriter(outFilename);
//print the results to the output file
output.println("mean = " + stats.getMean());
output.println("standard deviation = " + stats.getStdDev());
//close the output file
output.close();
}
}
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