I thought I had this figure out, and I was pretty confident it was going to work. Unfortunately, it did not.
The code below is supposed to return the average, the number of values entered and then calculate the std Var. I get it to return the average and count, but the std var result is off. Using the values 5, 6, 8 and 9 I am supposed to get a result of std var 1.83, I am getting something way off 7.17.
I know my error is in the way I am calculating the std Dev, but I was pretty sure I was doing it right.
Here is my code:
/**
This class is used to calculate the average and standard deviation
of a data set.
*/
public class DataSet{
private double sum;
private double sumSquare;
private int counter;
/**Constructs a DataSet object to hold the
* total number of inputs, sum and square
*/
public DataSet(){
sum = 0;
sumSquare = 0;
counter = 0;
}
/**Adds a value to this data set
* @param x the input value
*/
public void add(double x){
sum = sum + x;
sumSquare = sumSquare + x * x;
counter++;
}
/**Calculate average of dataset
* @return average, the average of the set
*/
public double getAverage(){
double avg = sum / counter;
return avg;
}
/**Get the total inputs values
* @return n, the total number of inputs
*/
public int getCount(){
return counter;
}
public double getStandardDeviation(){
double sqr = sumSquare / counter;
double stdDev = Math.sqrt(sqr);
return stdDev;
}
}
Here is my runner program:
import java.util.Scanner;
class DataSetRunner
{
public static void main(String[] args)
{
Scanner input = new Scanner(System.in);
DataSet data = new DataSet();
boolean done = false;
while (!done)
{
System.out.println("Enter value, Q to quit: ");
String userInput = input.next();
if (userInput.equalsIgnoreCase("Q"))
done = true;
else
{
double x = Double.parseDouble(userInput);
data.add(x);
}
}
System.out.println("Average = " + data.getAverage());
System.out.println("Count = " + data.getCount());
System.out.println("The Standard Deviation is = " + data.getStandardDeviation());
}
