java抽奖概率算法

package com.chinalife.action;

 

import java.math.BigDecimal;

import java.util.ArrayList;

import java.util.List;

import java.util.Random;

 

 

public class CJUtil{

 

static List<String> nn = new ArrayList<>();

private static String getResult(double ratePer){

String result = "未中奖";

String rt = String.valueOf(ratePer);

int decimals = rt.length()-rt.indexOf(".")-1; //小数位数

int up = getMaxDecimals(decimals).multiply(new BigDecimal(rt)).intValue(); //分子化为整数

int down = getMaxDecimals(decimals).multiply(new BigDecimal(100)).intValue(); //分母

Random rand = new Random();

int luckyNum = rand.nextInt(down);

if(luckyNum>=0 && luckyNum<up){

result = "中奖";

nn.add(String.valueOf(luckyNum));

}

 

System.out.println(result+"------"+luckyNum);

 

return result;

}

 

 

private static BigDecimal getMaxDecimals(int zeroNum){

String maxInt = "1";

for (int i = 0; i < zeroNum; i++) {

maxInt += "0";

}

BigDecimal bd = new BigDecimal(Integer.valueOf(maxInt));

return bd;

}

 

 

public static void main(String[] args){

int num = 0;

int tnum = 100;

double rate = 1; //百分比，即 xx%

for (int i = 0; i < tnum; i++) {

String r = getResult(rate);

if(r.equals("中奖")){

num += 1;

}

}

System.out.println("中奖率："+rate+"%-----"+"抽奖次数："+tnum+"-----"+"中奖次数："+num);

}

}