code: public synchronized void add(double x) {
  		final double oldA = a;
  		a += (x - a) / ++size;
  		q += (x - a) * (x - oldA);
  		min = Math.min(min, x);
  		max = Math.max(max, x);
  	}
docs: Adds a value to the stream.
  
  @param x the new value.