学习java随机验证码--方法一

public class 随机验证码 {
    public static void main(String[] args) {
        String code = createCode(5);
        System.out.println("随机验证码" + code);
    }

    public static String createCode(int n) {
        String code = "";
        Random r = new Random();
        for (int i = 0; i < n; i++) {
            int type = r.nextInt(3);
            switch (type) {
                case 0:
                    //大写字母 A:26  z:26+65
                    char ch = (char) (r.nextInt(26) + 65);
                    code += ch;
                    break;
                case 1:
                    //小写字母  a:97   z:97+25
                    char ch1 = (char) (r.nextInt(26) + 97);
                    code += ch1;
                    break;
                case 2:
                    //数字
                    code += r.nextInt(10);
                    break;
            }

        }
        return code;

    }
}