MixString

package com.company;

import java.util.Random;

public class Main {
    public static void main(String[] args) {
        StringBuilder s1 = new StringBuilder("0123456789");
        int length = s1.length();
        String s2 = "";
        int result = 0;

        Random r = new Random();

        for(int i = 0; i < length; i++){
            result = (int)(r.nextDouble() * s1.length());
            s2 += s1.charAt(result);
            s1.delete(result, result + 1);
        }
        System.out.println(s2);
    }
}