主要根据概率返回每次抽到的奖品，
以下是抽奖工具类
package com.ruoyi.project.dy.utils;
import java.util.ArrayList;
import java.util.List;
import java.util.Random;
/**
* @description:
* 抽奖工具类,概率和可以不等于1
* 概率为百分数去掉百分号的部分，如10%，则为10
* 抽奖操作如下：
* 1.输入抽奖概率集合，【抽奖概率集合为{10.0, 20.0, 30.0}】
* 2.生成连续集合， 【生成的连续集合为{(0.0, 10.0],(10.0, 30.0],(30.0, 60.0]}】
* 3.生成随机数， 【生成方法为 random.nextDouble() * maxElement】
* 4.判断随机数在哪个区间内，返回该区间的index【生成了随机数12.001，则它属于(10.0, 30.0]，返回 index = 1】
*
* */
public class LotteryUtil {
/**
* 定义一个连续集合
* 集合中元素x满足:(minElement,maxElement]
* 数学表达式为：minElement < x <= maxElement
*
*/
public class ContinuousList {
private double minElement;
private double maxElement;
public ContinuousList(double minElement, double maxElement){
if(minElement > maxElement){
throw new IllegalArgumentException("区间不合理，minElement不能大于maxElement！");
}
this.minElement = minElement;
this.maxElement = maxElement;
}
/**
* 判断当前集合是否包含特定元素
* @param element
* @return
*/
public boolean isContainKey(double element){
boolean flag = false;
if(element > minElement && element <= maxElement){
flag = true;
}
return flag;
}
}
private List<ContinuousList> lotteryList;
//概率连续集合
private double maxElement;
//这里只需要最大值，最小值默认为0.0
/**
* 构造抽奖集合
* @param list 为奖品的概率
*/
public LotteryUtil(List<Double> list){
lotteryList = new ArrayList<ContinuousList>();
if(list.size() == 0){
throw new IllegalArgumentException("抽奖集合不能为空！");
}
double minElement = 0d;
ContinuousList continuousList = null;
for(Double d : list){
minElement = maxElement;
maxElement = maxElement + d;
continuousList = new ContinuousList(minElement, maxElement);
lotteryList.add(continuousList);
}
}
/**
* 进行抽奖操作
* 返回：奖品的概率list集合中的下标
*/
public int randomColunmIndex(){
int index = -1;
Random r = new Random();
double d = r.nextDouble() * maxElement;
//生成0-1间的随机数
if(d == 0d){
d = r.nextDouble() * maxElement;
//防止生成0.0
}
int size = lotteryList.size();
for(int i = 0; i < size; i++){
ContinuousList cl = lotteryList.get(i);
if(cl.isContainKey(d)){
index = i;
break;
}
}
if(index == -1){
throw new IllegalArgumentException("概率集合设置不合理！");
}
return index;
}
public double getMaxElement() {
return maxElement;
}
public List<ContinuousList> getLotteryList() {
return lotteryList;
}
public void setLotteryList(List<ContinuousList> lotteryList) {
this.lotteryList = lotteryList;
}
}
该工具类的基本思想是，将抽奖概率分布到数轴上，如现有三个抽奖概率10、20、30，将三者依次添加到概率集合中，则构造的数轴为：010范围内表示概率10，1030范围内表示概率为20，3060范围内表示概率为30，数轴上的长度对应着相应的概率。由这种处理方式可知，概率总和并不需要等于1。该工具类的成功与否在于Random.nextDouble()能否等概率地生成01之间的任意一个数。
对该抽奖工具进行测试，测试类如下：
package com.ruoyi.project.dy.utils;
/**
* @description:
*/
public class Result {
private int index;
private int sumTime;
private int time;
private double probability;
private double realProbability;
public int getIndex() {
return index;
}
public void setIndex(int index) {
this.index = index;
}
public int getTime() {
return time;
}
public void setTime(int time) {
this.time = time;
}
public int getSumTime() {
return sumTime;
}
public void setSumTime(int sumTime) {
this.sumTime = sumTime;
}
public double getProbability() {
return probability;
}
public double getRealProbability() {
return realProbability;
}
public void setRealProbability(double realProbability) {
this.realProbability = realProbability;
}
public Result(){
}
public Result(int index, int sumTime, int time, double realProbability) {
this.setIndex(index);
this.setTime(time);
this.setSumTime(sumTime);
this.setRealProbability(realProbability);
}
@Override
public String toString(){
return "索引值：" + index + "，抽奖总数：" + sumTime + "，抽中次数：" + time + "，概率："
+ realProbability + "，实际概率：" + (double)time/sumTime;
}
}
//----------------------------------
package com.ruoyi.project.dy.utils;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
/**
* @description: 测试抽奖工具
*/
public class TestLottery {
static final int TIME = 1000000;
public static void iteratorMap(Map<Integer, Integer> map, List<Double> list){
for(Map.Entry<Integer, Integer> entry : map.entrySet()){
int index = entry.getKey();
int time = entry.getValue();
Result result = new Result(index, TIME, time, list.get(index));
System.out.println(result);
}
}
public static void main(String[] args) {
//构造概率集合
List<Double> list = new ArrayList<Double>();
list.add(90d);
list.add(4d);
list.add(3d);
list.add(2d);
list.add(1d);
LotteryUtil ll = new LotteryUtil(list);
double sumProbability = ll.getMaxElement();
Map<Integer, Integer> map = new HashMap<Integer, Integer>();
for(int i = 0; i < TIME; i++){
int index = ll.randomColunmIndex();
if(map.containsKey(index)){
map.put(index, map.get(index) + 1);
}else{
map.put(index, 1);
}
}
for(int i = 0; i < list.size(); i++){
double probability = list.get(i) / sumProbability;
list.set(i, probability);
}
iteratorMap(map, list);
}
}
调用方式
public LotteryUtil(List<Double> list)
传入参数作为概率集合
public int randomColunmIndex()
进行抽奖操作，返回List集合中索引下标
测试结果：
