生成若干位數的隨機ID的Java工具類

寫了如下工具類：

    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();

        }


}  </pre> 


 以生成10位隨機數為例：
    public class Producer {  
        public static String generateIdOfTen() {  
            String randomNumber = SystemUtil.getRandomNumberByNum(10);  
            long time = System.currentTimeMillis();  
            return time + randomNumber;  
        }  
    }