/**
 * 獎品實體類
 */
public class Award{
  public Award(){}
  public Award(String awardTitle,double probability){
    this.awardTitle = awardTitle;
    this.probability = probability;
  }
  /**獎品ID**/
  private String awardId;
  /**獎品名**/
  private String awardTitle;
  /**中獎概率**/
  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;
  }
}

public class LotteryUtil {

  /**
   * 抽獎，獲取中獎獎品
   * @param awardList 獎品及中獎概率列表
   * @return 中獎商品
   */
  public static Award lottery(List<Award> awardList) {
    if(awardList.isEmpty()){
      throw new AwardListIsEmptyException();
    }
    //獎品總數(shù)
    int size = awardList.size();

    //計算總概率
    double sumProbability = 0d;
    for (Award award : awardList) {
      sumProbability += award.getProbability();
    }

    //計算每個獎品的概率區(qū)間
    //例如獎品A概率區(qū)間0-0.1 獎品B概率區(qū)間 0.1-0.5 獎品C概率區(qū)間0.5-1
    //每個獎品的中獎率越大，所占的概率區(qū)間就越大
    List<Double> sortAwardProbabilityList = new ArrayList<Double>(size);
    Double tempSumProbability = 0d;
    for (Award award : awardList) {
      tempSumProbability += award.getProbability();
      sortAwardProbabilityList.add(tempSumProbability / sumProbability);
    }

    //產(chǎn)生0-1之間的隨機(jī)數(shù)
    //隨機(jī)數(shù)在哪個概率區(qū)間內(nèi)，則是哪個獎品
    double randomDouble = Math.random();
    //加入到概率區(qū)間中，排序后，返回的下標(biāo)則是awardList中中獎的下標(biāo)
    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>();
    awardList.add(new Award("10個積分",0.35d));
    awardList.add(new Award("33個積分",0.25d));
    awardList.add(new Award("5元紅包",0.002d));
    awardList.add(new Award("20元話費",0.003d));
    awardList.add(new Award("京東100元購物卡",0.0005d));
    awardList.add(new Award("未中獎",0.1d));

    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);
    }
  }
}