Java Utililty Methods Collection Sum

return sum(numbers, false);

double total = 0.;
for (double value : collection)
    total += value;
return total;

double sum = 0.0;
for (Double elem : list) {
    sum += elem;
return sum;

double ret = 0;
for (Double d : values)
    ret += d;
return ret;

if (values == null || values.isEmpty()) {
    return 0L;
double sum = 0;
for (Double value : values) {
    sum += value;
return sum;
...

List<Double> filteredValues = filterNulls(values);
if (filteredValues.size() == 0)
    return null;
double sum = 0;
for (Double value : filteredValues) {
    sum += value;
return sum;
...

double sum = 0.0;
for (Double value : values) {
    sum += value;
return sum;

Iterator<double[]> iter = vec.iterator();
if (vec.size() <= 0)
    return null;
double[] res = new double[iter.next().length];
while (iter.hasNext()) {
    double[] tmp = iter.next();
    for (int i = 0; i < res.length; i++) {
        res[i] += tmp[i];
...

int sum = 0;
for (Integer i : values) {
    sum = sum + i;
return sum;

double sum = 0;
for (N number : collection) {
    sum += number.doubleValue();
return sum;