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package org.usc.usc.lottery;  public class Gift {     private int index;     private String gitfId;     private String giftName;     private double probability;      public Gift(int index, String gitfId, String giftName, double probability) {         this.index = index;         this.gitfId = gitfId;         this.giftName = giftName;         this.probability = probability;     }      public int getIndex() {         return index;     }      public void setIndex(int index) {         this.index = index;     }      public String getGitfId() {         return gitfId;     }      public void setGitfId(String gitfId) {         this.gitfId = gitfId;     }      public String getGiftName() {         return giftName;     }      public void setGiftName(String giftName) {         this.giftName = giftName;     }      public double getProbability() {         return probability;     }      public void setProbability(double probability) {         this.probability = probability;     }      @Override     public String toString() {         return "Gift [index=" + index + ", gitfId=" + gitfId + ", giftName=" + giftName + ", probability=" + probability + "]";     }  } 

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package org.usc.usc.lottery;  import java.util.ArrayList; import java.util.Collections; import java.util.List; import java.util.Random;  /**  * 不同概率抽奖工具包  *  * @author Shunli  */ public class LotteryUtil {     private static final Random random = new Random();      /**      * 抽奖      *      * @param orignalRates      *            原始的概率列表，保证顺序和实际物品对应      * @return      *         物品的索引      */     public static int lottery(List<Double> orignalRates) {         if (orignalRates == null || orignalRates.isEmpty()) {             return -1;         }          int size = orignalRates.size();          List<Double> sortOrignalRates = new ArrayList<Double>(size);         sortOrignalRates.addAll(orignalRates);         Collections.sort(sortOrignalRates);          List<Double> rates = new ArrayList<Double>(size);         // 计算总概率，这样可以保证不一定总概率是1         double sumRate = 0d;         for (double rate : sortOrignalRates) {             sumRate += rate;         }          // 计算每个物品在总概率的基础下的概率情况         Double tempSumRate = 0d;         for (double rate : sortOrignalRates) {             tempSumRate += rate;             rates.add(tempSumRate / sumRate);         }          double result = rates.get(0);         double nextDouble = random.nextDouble();          for (double rate : rates) {             if (nextDouble >= rate) {                 continue;             }             result = rate;             break;         }          // 根据区块值来获取抽取到的物品索引         int index = rates.indexOf(result);         int orignalIndex = orignalRates.indexOf(sortOrignalRates.get(index));          return orignalIndex;     } } 

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package org.usc.usc.lottery;  import java.util.ArrayList; import java.util.HashMap; import java.util.List; import java.util.Map; import java.util.Map.Entry;  /**  * 不同概率抽奖  *  * @author ShunLi  */ public class LotteryTest {     public static void main(String[] args) {         List<Gift> gifts = new ArrayList<Gift>();         // 序号==物品Id==物品名称==概率         gifts.add(new Gift(1, "P1", "物品1", 0.2d));         gifts.add(new Gift(2, "P2", "物品2", 0.1d));         gifts.add(new Gift(3, "P3", "物品3", 0.4d));         gifts.add(new Gift(4, "P4", "物品4", 0.3d));         gifts.add(new Gift(5, "P5", "物品5", 0d));         gifts.add(new Gift(6, "P6", "物品6", -0.1d));         gifts.add(new Gift(7, "P7", "物品7", 0.008d));          List<Double> orignalRates = new ArrayList<Double>(gifts.size());         for (Gift gift : gifts) {             double probability = gift.getProbability();             if (probability < 0) {                 probability = 0;             }             orignalRates.add(probability);         }          // // test         // for (int i = 0; i < 10000; i++) {         // try {         // Gift tuple = gifts.get(LotteryUtil.lottery(orignalRates));         // System.out.println(tuple);         // } catch (Exception e) {         // System.out.println("lottery failed, please check it!");         // }         // }          // statistics         Map<Integer, Integer> count = new HashMap<Integer, Integer>();         double num = 1000000;         for (int i = 0; i < num; i++) {             int orignalIndex = LotteryUtil.lottery(orignalRates);              Integer value = count.get(orignalIndex);             count.put(orignalIndex, value == null ? 1 : value + 1);         }          for (Entry<Integer, Integer> entry : count.entrySet()) {             System.out.println(gifts.get(entry.getKey()) + ", count=" + entry.getValue() + ", probability=" + entry.getValue() / num);         }     }  } 

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Gift [index=1, gitfId=P1, giftName=物品1, probability=0.2], count=199139, probability=0.199139 Gift [index=2, gitfId=P2, giftName=物品2, probability=0.1], count=99328, probability=0.099328 Gift [index=3, gitfId=P3, giftName=物品3, probability=0.4], count=396575, probability=0.396575 Gift [index=4, gitfId=P4, giftName=物品4, probability=0.3], count=296997, probability=0.296997 Gift [index=7, gitfId=P7, giftName=物品7, probability=0.0080], count=7961, probability=0.007961