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) )+" ");
                  }