学习练习 java 验证码练习

1 String str="1234567890qwertyuioplkjhgfdsazxcvbnmQWERTYUIOPLKJHGFDSAZXCVBNM    ";
2                   int b[]=new int[4];
3                  Random a =new Random();
4                   for(int i=0;i<4;i++)
5                   {
6                      b[i]=a.nextInt(62);
7                  System.out.print(str.substring((b[i]),(b[i]+1) )+" ");
8                  }