概率抽奖

之前看到的一个概率抽奖的方法，忘记出处了。整理到我的博客，方便自己查看

import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;

public class LotteryUtil {

    /**
     * 抽奖，获取中奖奖品
     * @param awardList 奖品及中奖概率列表
     * @return 中奖商品
     */
    public static Award lottery(List<Award> awardList) {
        if(awardList.isEmpty()){
            throw new RuntimeException();
        }
        //奖品总数
        int size = awardList.size();

        //计算总概率
        double sumProbability = 0d;
        for (Award award : awardList) {
            sumProbability += award.getProbability();
        }

        //计算每个奖品的概率区间
        //例如奖品A概率区间0-0.1  奖品B概率区间 0.1-0.5 奖品C概率区间0.5-1
        //每个奖品的中奖率越大，所占的概率区间就越大
        List<Double> sortAwardProbabilityList = new ArrayList<Double>(size);
        Double tempSumProbability = 0d;
        for (Award award : awardList) {
            tempSumProbability += award.getProbability();
            sortAwardProbabilityList.add(tempSumProbability / sumProbability);
        }

        //产生0-1之间的随机数
        //随机数在哪个概率区间内，则是哪个奖品
        double randomDouble = Math.random();
        //加入到概率区间中，排序后，返回的下标则是awardList中中奖的下标
        sortAwardProbabilityList.add(randomDouble);
        Collections.sort(sortAwardProbabilityList);
        int lotteryIndex = sortAwardProbabilityList.indexOf(randomDouble);
        return awardList.get(lotteryIndex);
    }

    public static void main(String[] args) {
        List<Award> awardList = new ArrayList<Award>();
        /*
         * 使用以下方法 或者将 内部类Award定义为静态的
        LotteryUtil lottery = new LotteryUtil();
        awardList.add(lottery.new Award("10个积分",0.35d));
        */
        awardList.add(new Award("10个积分",0.35d));
        awardList.add(new Award("33个积分",0.25d));
        awardList.add(new Award("5元红包",0.1d));
        awardList.add(new Award("20元话费",0.05d));
        awardList.add(new Award("京东100元购物卡",0.0005d));
        awardList.add(new Award("未中奖",0.2495d));
        System.out.println(0.35+0.25+0.1+0.05+0.0005+0.2495);
        Map<String,Integer> result = new HashMap<String,Integer>();
        for(int i=0;i<10000;i++){
            Award award = lottery(awardList);
            String title = award.getAwardTitle();
            Integer count = result.get(title);
            result.put(title, count == null ? 1 : count + 1);
        }

        for (Entry<String, Integer> entry : result.entrySet()) {
            System.out.println(entry.getKey() + ", count=" + entry.getValue() +", reate="+ entry.getValue()/10000d);
        }
    }
    
   static class Award{
        public Award(){}
        public Award(String awardTitle,double probability){
            this.awardTitle = awardTitle;
            this.probability = probability;
        }
        /**奖品ID**/
        private String awardId;
        /**奖品名**/
        private String awardTitle;
        /**中奖概率**/
        private double probability;
        public String getAwardId() {
            return awardId;
        }
        public void setAwardId(String awardId) {
            this.awardId = awardId;
        }
        public String getAwardTitle() {
            return awardTitle;
        }
        public void setAwardTitle(String awardTitle) {
            this.awardTitle = awardTitle;
        }
        public double getProbability() {
            return probability;
        }
        public void setProbability(double probability) {
            this.probability = probability;
        }
    }
}