生成若干位数的随机ID的Java工具类详解编程语言

写了如下工具类：

    public class SystemUtil {   
        public static String getRandomNumberByNum(int num) {   
            StringBuffer sb = new StringBuffer();   
            for (int i = 0; i < num; i++) {   
                long randomNum = Math.round(Math.floor(Math.random() * 10.0D));   
                sb.append(randomNum);   
            }   
            return sb.toString();   
        }   
       
           
    }  

以生成10位随机数为例：

    public class Producer {   
        public static String generateIdOfTen() {   
            String randomNumber = SystemUtil.getRandomNumberByNum(10);   
            long time = System.currentTimeMillis();   
            return time + randomNumber;   
        }   
    }