Java Random随机生成验证码

public static void main(String[] args)
    {
        char[] chs=new char[52];
        for (int i = 0; i < chs.length; i++)
        {
            if(i<=25) chs[i]=(char)(97+i);
            else chs[i]=(char)(65+i-26);
        }
//      for (int i = 0; i < chs.length; i++)
//      {
//          System.out.println(chs[i]);
//      }
        Random r=new Random();
        StringBuilder result=new StringBuilder();
        for (int i = 0; i < 4; i++)
        {
            result.append(chs[r.nextInt(chs.length)]);//随机生成一个大小写字母数组索引进行访问
        }
        result.append(r.nextInt(10));//随机生成0-9的数字
        System.out.println(result);
        String Input;
        String yanzhenma= result.toString();
        System.out.print("请输入验证码:");
        Scanner sc=new Scanner(System.in);
        Input=sc.next();
        if(Input.equals(yanzhenma)) System.out.println("验证成功！");
        else System.out.println("验证码错误");
    }