学习练习 java 验证码练习

String str="1234567890qwertyuioplkjhgfdsazxcvbnmQWERTYUIOPLKJHGFDSAZXCVBNM    ";
                  int b[]=new int[4];
                 Random a =new Random();
                  for(int i=0;i<4;i++)
                  {
                     b[i]=a.nextInt(62);
                 System.out.print(str.substring((b[i]),(b[i]+1) )+" ");
                 }