sclass RollingAverage {
  int windowSize = 50;
  int recalcEvery = 1000; // to counter floating point errors
  new LinkedList<Double> list;
  double sum;
  int n;
  
  *() {}
  *(int *windowSize) {}
  
  synchronized void add(double d) {
    if (++n >= recalcEvery) {
      n = 0;
      sum = doubleSum(list);
    }
    
    if (l(list) >= windowSize)
      sum -= popFirst(list);
      
    list.add(d);
    sum += d;
  }
  
  synchronized double get() {
    ret doubleRatio(sum, l(list));
  }
}