java字符串直接+会出错

Calendar calendar = Calendar.getInstance();
        calendar.setFirstDayOfWeek(Calendar.MONDAY);//设置星期一为一周开始的第一天
        calendar.setMinimalDaysInFirstWeek(4);//可以不用设置
        calendar.setTimeInMillis(System.currentTimeMillis());//获得当前的时间戳
        int weekYear = calendar.get(Calendar.YEAR);//获得当前的年
        int weekOfYear = calendar.get(Calendar.WEEK_OF_YEAR);//获得当前日期属于今年的第几周
        System.err.println("myCarWashCard.getMyCarWashCardId() + weekYear + weekOfYear：" + myCarWashCard.getMyCarWashCardId() + weekYear + weekOfYear + "");
        carWashRecord.setCarWashRecordOnlySn(myCarWashCard.getMyCarWashCardId() + weekYear + weekOfYear + "");

这个会出错，有可能先计算，在出字符串。也有可能会出整 个字符串。