javaSE编程思想

验证码

 public static void main(String[] args) {
   String code =  createCode(5);
        System.out.println(code);
    }
    public static String createCode(int n) {
        Random r = new Random();
        String code = "";
        for (int i = 0; i <n ; i++) {
            int type = r.nextInt(3);//生成随机数 0 1 2
            switch(type){
                case 0:
                    //大写字母
                    char ch = (char)(r.nextInt(26)+65);
                    code+=ch;
                    break;
                case 1:
                    //小写字母
                    char CH = (char)(r.nextInt(26)+97);
                    code+=CH;
                    break;
                case 2:
                    //大写字母
                  int num = r.nextInt(10);//0-9
                    code+=num;
                    break;
            }
        }
        return code;
        }