Java计算方差算法实例分享

目前java这个版本没有直接计算方差的封装方法，只能自己写算法：

package com.tim.math;

import java.util.Random;
import java.util.stream.DoubleStream;

public class Variance {

	private static final Random rand = new Random();
	private static final int MIN = 1;
	private static final int MAX = 140;
	private static final int POPULATION_SIZE = 30_000_000;
	public static final int NUMBER_OF_RUNS = 20;

	public static void main(String... args) {
		double[] population = DoubleStream.generate(Variance::randInt).limit(POPULATION_SIZE).toArray();
		System.out.println("方差="+varianceImperative(population));
	}

	public static int randInt() {
		return rand.nextInt((MAX - MIN) + 1) + MIN;
	}

	public static double varianceImperative(double[] population) {
		double average = 0.0;
		for (double p : population) {
			average += p;
		}
		average /= population.length;

		double variance = 0.0;
		for (double p : population) {
			variance += (p - average) * (p - average);
		}
		return variance / population.length;
	}
}