请输入验证码

           String str11 = "abcdefghijklmnopqrstuvwxyz";
           String str12 = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
           String str13 = "12345678901234567890123456";
           System.out.println("请输入验证码：");
           for(int x = 1; x <= 4; x++)
           {
               Random a = new Random();
               Random b = new Random();
               Random c = new Random();
               Random d = new Random();
               int m = a.nextInt(26);
               int f = c.nextInt(26);
               int e = d.nextInt(26);
               int n = b.nextInt(3);
               if(n == 0)
               {
                   System.out.print(str11.charAt(e) + " ");
               }
               else if(n == 1)
               {
                   System.out.print(str12.charAt(f) + " ");
               }
               else if(n == 2)
               {
                   System.out.print(str13.charAt(m) + " ");
               }
           }