Java Utililty Methods List Variance

return variance(doubleArrayList.stream().mapToDouble(Double::doubleValue).toArray());

long n = 0;
double mean = mean(list);
double s = 0.0;
for (double x : list) {
    n++;
    double delta = x - mean;
    mean += delta / n;
    s += delta * (x - mean);
...

double mean = mean(data);
double sum = 0;
double diff = 0;
for (Double d : data) {
    diff = d - mean;
    sum += (diff * diff);
return sum / data.size();
...

double mean = average(observations);
double varSum = 0.0;
for (double d : observations) {
    varSum += (d - mean) * (d - mean);
return varSum / observations.size();

float mean = mean(values);
float variance = 0;
for (float value : values) {
    variance += Math.pow(value - mean, 2);
variance = variance / ((float) values.size());
return variance;

int n = data.size();
double sum = 0;
double avg = sum(data) / ((double) n);
for (int d : data) {
    sum += (d - avg) * (d - avg);
return sum / n;