Just another update

Task/Standard-deviation/Java/standard-deviation.java

@@ -1,39 +1,22 @@
-import java.util.LinkedList;
 public class StdDev {
-    LinkedList<Double> nums;
-    public StdDev() {
-        nums = new LinkedList<Double>();
+    int n = 0;
+    double sum = 0;
+    double sum2 = 0;
+
+    public double sd(double x) {
+	n++;
+	sum += x;
+	sum2 += x*x;
+
+	return Math.sqrt(sum2/n - sum*sum/n/n);
     }
+
     public static void main(String[] args) {
         double[] testData = {2,4,4,4,5,5,7,9};
         StdDev sd = new StdDev();
 
         for (double x : testData) {
-            sd.newNum(x);
-            System.out.println(sd.getSD());
+            System.out.println(sd.sd(x));
         }
     }
-
-    public void newNum(double num) {
-        nums.add(num);
-    }
-
-    public double getAvg() {
-        if (nums.isEmpty()) return 0;
-        double ret = 0;
-        double sum = 0;
-        for (double num : nums) {
-           sum += num;
-        }
-        return sum / nums.size();
-    }
-
-    public double getSD() {
-        double sqDiffs = 0;
-        double avg = getAvg();
-        for (double num : nums) {
-           sqDiffs += (num - avg) * (num - avg);
-        }
-        return Math.sqrt(sqDiffs / nums.size());
-    }
 }