public  Reward getRand(){
        int arrSum = getArrSum(rewards);
        Reward result = null;
        if(arrSum <= 0){
            return result;
        }
        if(rewards != null && rewards.size() > 0){
            for(int i=0;i<rewards.size();i++){
                Random random = new Random();
                int randNum = random.nextInt(arrSum);
                int compareNum = randNum + 1;  //中奖概率范围为 [1,arrSum]
                if(compareNum <= rewards.get(i).getSuccPercent()){
                    result = rewards.get(i);
                    break;
                }else{
                    arrSum -= rewards.get(i).getSuccPercent();
                }
            }
        }

        return result;
    }