# Object-Oriented Programming with Java, part I – Exercise 67

This program calculates the variance from a series of numbers in an array list.

## My Code

``````import java.util.ArrayList;

public class Variance {

// Copy here sum from exercise 63
public static int sum(ArrayList<Integer> list) {
int tot = 0;
for (int num : list) {
tot = tot + num;
}
}

// Copy here average from exercise 64
public static double average(ArrayList<Integer> list) {
int tot = 0;
int i = 0;
for (int num : list) {
tot = tot + num;
i++;
}
return (double)tot / i;
}

public static double variance(ArrayList<Integer> list) {
// write code here
double var = 0;
double avg = average(list);
for (double num : list) {
var = var + ((num - avg) * (num - avg));
}
var = var/(list.size() -1);
return var;
}

public static void main(String[] args) {
ArrayList<Integer> list = new ArrayList<Integer>();

System.out.println("The variance is: " + variance(list));
}

}``````

## Model Code

``````import java.util.ArrayList;

public class Variance {

// Copy here sum from exercise 63

public static int sum(ArrayList<Integer> list) {

int sum = 0;

for (int number : list) {

sum = sum + number;

}

return sum;

}

// Copy here average from exercise 64

public static double average(ArrayList<Integer> list) {

double sum = (double) sum(list);

return sum / list.size();

}

public static double variance(ArrayList<Integer> list) {

// write code here

double aver = average(list);

double var = 0;

for (int number : list) {

double difference = number - aver;

double squareOfDifference = difference * difference;

var = var + squareOfDifference;

}

var = var / (list.size() - 1);

return var;

}

public static void main(String[] args) {

ArrayList<Integer> list = new ArrayList<Integer>();

System.out.println("The variance is: " + variance(list));

}

}``````