Perf.java

// ---------
// VERSION 1
// ---------
public void sum1(List<Iterator<Double>> iterators, int length) {
  double[] data = new double[length];

  for (Iterator<Double> it : iterators) {
    for (int i = 0; i < length; i++) {
      data[i] += it.next();
    }
  }

  return data;
}

// ---------
// VERSION 2
// ---------
public void sum2(List<Iterator<Double>> iterators, int length) {
  double[] data = new double[length];

  for (int i = 0; i < length; i++) {
    for (Iterator<Double> it : iterators) {
      data[i] += it.next();
    }
  }

  return data;
}