随机取四个数组成字符串

随机取4个数组成字符串
import java.util.Random;

public class MyRandom1 {

public static void main(String[] args) {
int i = 0;
int j = 0;
String s = "";
//double d=Math.random();另一种获取随机数的方法
//int i=(int)(d*10);
Random rn = new Random();
do {
j = rn.nextInt(10);
String s1 = String.valueOf(j);
if (!s.contains(s1)) {
s = s + s1;
i++;
}

} while (i != 4);

System.out.println(s);
}
}