设置验证码

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import java.util.Arrays; import java.util.Random; import java.util.Scanner;   public class Test1 {     public int len;     public String arr2;     public char arr1;      public char string[] = {'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f', 'g',             'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z',             '1', '2', '3', '4', '5', '6', '7', '8', '9', '0'};       /*练习1.随机数：设计一个方法，返回随机字符串长度由用户输入     //public class Codeutil{     //返回的字符串包含数字和字母，长度必须6-10之间     如果len<6返回长度为6，     如果len>10,则返回长度为10          */     public static void main(String[] args) {           Scanner a = new Scanner(System.in);         System.out.println("请输入验证码长度：");         String b = a.nextLine();         int len = Integer.parseInt(b);         Test1 test1 = new Test1();         String arr = test1.randomNumber(len);         System.out.println(arr);       }     public String randomNumber(int c ){               if(c<6 ||c>10){                 String s="输入错误，请重新输入！";                 return s;               } else{                 char[] arr1=new char[c];                 for(int k=0;k<=c-1;k++){                     Random random=new Random();                        arr1[k]=string[random.nextInt(62)];                   }                   String arr2 = String.valueOf(arr1);                   return arr2;         }           } }