java编程求和、平均值、方差、标准差

这里实现了java编程求和、平均值、方差、标准差，求标准差的时候使用到了java提供的方法求算术平方根。

改天利用算法自己编写一个算术平方根，先贴上以上几种求法，方法的复用性和拓展性就不写了---这里只有求平均数两种情况的方法写了。

package com.math;

/**
 * 
 * @author cisco lee
 * @version 1.0
 * Mathematical Analysis Encyclopedia
 * {@link https://baike.baidu.com/item/%E6%95%B0%E5%AD%A6%E5%88%86%E6%9E%90/3123?fr=aladdin}
 * 
 * 
 */
public class MathAnalyse {
    public static void main(String[] args) {
        AddThread addobject = new AddThread();
        Avg avgobject = new Avg();
        Variance varobject = new Variance();
        StandardDeviation standardobject = new StandardDeviation();
        double []a = new double[5];
        System.out.println("all a[i]:");
        for (int i = 0; i <a.length; i++) {
            a[i]=i+2;//2,3,4,5,6
            System.out.print(a[i]+" ");
        }
        System.out.println();
        double sum = addobject.add(a);
        double average = avgobject.avg(sum,5);
        double var = varobject.populationVariance(a, average);
        standardobject.standardDeviation(var);
        addobject.start();
        avgobject.start();
        varobject.start();
        standardobject.start();    
    }
}

//this is a class of summation methods.
class AddThread extends Thread {
    double thisresult=0;
    public double add(double []result){
        for (int i = 0; i <result.length; i++) {
            thisresult=result[i]+thisresult;
        }
        return thisresult;
    }
    public void run() {
        // TODO Auto-generated method stub
        System.out.println("sum:"+thisresult);
    }
}

//This is a class of averaging methods.
class Avg extends Thread{
    double avg=0;
    public double avg(double sum,int num){
        avg = sum/num;
        return avg;
    }
    public double avg(double[]sum){
        for (int i = 0; i < sum.length; i++) {
            avg = sum[i]+avg;
        }
        return avg;
    }
    public void run() {
        // TODO Auto-generated method stub
        System.out.println("average:"+avg);
    }
}

//Calculation variance #求方差
class Variance extends Thread{
    double variance=0;
    /**
     * This is a method of calculating variance to know of the population sample。 #这是一个计算知道总体样本的方法
     * @param a This is a Sample。 #这是一个样本
     * @param avg this is the average of the sample. #这是样本的平均值
     * @return variance
     * Pay attention: a.length This is the number of sample. #这是样本成员个数
     */
    public double populationVariance(double[]a,double avg) {
        for (int j = 0; j < a.length; j++) {
            variance =((a[j]-avg)*(a[j]-avg))+variance;
        }
        variance = variance/a.length;
        return variance;
    }
    public void run() {
        // TODO Auto-generated method stub
        System.out.println("Variance:"+variance);;
    }
}

//Sdandard deviation
class StandardDeviation extends Thread{
    double stand;
    public double standardDeviation( double variance) {
        stand = Math.sqrt(variance);
        return stand;
    }
    public void run() {
        // TODO Auto-generated method stub
        System.out.println("StandardDeviation:"+stand);
    }
}

拓展：

求算术平方根的算法：

求√A 的算法：
输入正数A
令X=A/2
(1) Y=(X+A/X)/2
如果|Y-X|<ε（你要求的精确度），则打印Y，就是√A ，结束
否则，令X=Y，执行语句(1)
用QBASIC语言写：
INPUT A
X=A/2

下面，是使用java编写的算术平方根：

【后面加上，休息...】