Java 中随机生成规定位数的随机数

在很多编写代码的过程中都会涉及到需要生成随机数，其中已生成6位的短信随机数较多，一下是我分享的两个案例。

import java.util.Random;

public class Test {

public static String testNum(int num){
StringBuilder str=new StringBuilder();//定义变长字符串
Random random=new Random();
for (int i = 0; i < num; i++) {
str.append(random.nextInt(10));
}
return str.toString();
}

}

public static String testNum(int num) {
String[] vec = { "0", "1", "2", "3", "4", "5", "6", "7", "8", "9" };
num = num <= 0 ? 1 : num;
StringBuffer str = new StringBuffer(10);
for (int i = 0; i < num; i++) {
int r1 = Long.valueOf(Math.round(Math.random() * (vec.length - 1))).intValue();
str.append(vec[r1]);
}
return str.toString();
}

String code = Test.testNum(6);
System.out.println(code);