import java.math.BigDecimal;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
/**
 * @PACKAGE_NAME.Test 
* 日期： 2017/5/3
 * 描述：
*/
public class Test {

    /**
     * 所有所有獎品
*/
public enum Trophy {

        A("獎品-A", new BigDecimal(0.889)),
B("獎品-B", new BigDecimal(0.1)),
C("獎品-C", new 
 
BigDecimal(0.01)),
D("獎品-D", new BigDecimal(0.001)),;
        public String name;
        public BigDecimal probably;
Trophy(String name, BigDecimal probably) {
            this.name = name;
            this.probably = probably;
}
    }

    /**
     * 獲取一個隨機數
*
     * @param min 最大值
* @param max 最小值
* @return
 
*/
public int getRandomInt(int min, int max) {
        return (int) Math.round(Math.random() * (max - min) + min);
}

    /**
     * 獲取隨機數的最大值
*
     * @param trophies 所有獎品
* @return
*/
public int getMaxRandomInt(List<Trophy> trophies) {
        BigDecimal minProbably = trophies.stream().min((x, 
 
y) -> x.probably.compareTo(y.probably)).get().probably;
String[] split = (minProbably.doubleValue() + "").trim().split("\\.");
        return (int) Math.pow(10, split[split.length - 1].length());
}

    /**
     * 抽獎
*
     * 隨機一個數，判斷在哪個獎品的區間內
*
     * @return
*/
public Trophy draw() {
        Trophy trophy = null;
        int maxInt = getMaxRandomInt(Arrays.asList(Trophy.values()));
        int random = getRandomInt(1, maxInt), start = 0;
        for (Trophy trophy1 : Trophy.values()) {
            int end = start + (int) (trophy1.probably.doubleValue() * maxInt);
            if (random > start && random <= end) {
                trophy = trophy1;
                break;
} else {
                start = end;
}
        }
        return trophy;
}

    @org.junit.Test
public void test() {
        List<Trophy> trophyList = new ArrayList<>();
        for (int i = 0; i < 10000; i++) {
            Trophy trophy = draw();
            if (trophy != null) {
                trophyList.add(trophy);
}
        }

        //計算各個抽中次數
for (Trophy trophy : Trophy.values()) {
            System.out.println("抽中 " + trophy.name + " 數量："
+ trophyList.stream().filter(trophy1 -> trophy1.equals(trophy)).count());
}
    }
}