如何计算C ++或Java中的方差，中位数和标准差？

public class Statistics {
double[] data;
int size;

    public Statistics(double[] data) {        this.data = data;        size = data.length;    }    double getMean() {        double sum = 0.0;        for(double a : data) sum += a;        return sum/size;    }    double getVariance() {        double mean = getMean();        double temp = 0;        for(double a :data) temp += (a-mean)*(a-mean);        return temp/(size-1);    }    double getStdDev() {        return Math.sqrt(getVariance());    }    public double median() {       Arrays.sort(data);       if (data.length % 2 == 0)          return (data[(data.length / 2) - 1] + data[data.length / 2]) / 2.0;       return data[data.length / 2];    }}