import java.util.Random;

public class CreateRandomData {

    // 生成随机数字和字母,
    public String getStringRandom(int length) {

        String val = "";
        Random random = new Random();

        // 参数length，表示生成几位随机数
        for (int i = 0; i < length; i++) {

            String charOrNum = random.nextInt(2) % 2 == 0 ? "char" : "char";
            // 输出字母
            if ("char".equalsIgnoreCase(charOrNum)) {
               
                int temp = random.nextInt(2) % 2 == 0 ? 65 : 97;
                val += (char) (random.nextInt(26) + temp);
            } else if ("num".equalsIgnoreCase(charOrNum)) {
                val += String.valueOf(random.nextInt(10));
            }
        }
        return val;
    }

    public static void main(String[] args) {
        CreateRandomData test = new CreateRandomData();
        // 测试
        System.out.println(test.getStringRandom(12));
    }
}