Exercise 3. (Variance for accumulator) Validate that the following code, which adds the methods var and stddev) to Accumulator, computes both the mean and variance of the numbers presented as arguments to addDataValue): public class Accumulator i private double m; private double s private int N; public void addDataValue (double x) i s=s+1.0 * (N-1) / N * (x-m) * (x-m); m m + (x -m) N public double mean)return m; ) public double var return s/(N-1) public double stddev) return Math.sqrt (this.var))