Java 随机生成4位数字验证码

import java.util.Random;
/**
 * Created with IntelliJ IDEA.
 *
 * @Author: twx
 * @Date: 2021/09/24/10:01
 * @Description: 随机生成4位数字验证码
 */
public class TestGenerate4RandomNumber {
    public static void main(String[] args) {
        //定义取值范围
        String str = "0123456789";
        //容量为4
        StringBuilder sb = new StringBuilder(4);
        for (int i = 0; i < 4; i++) {
            //遍历4次，拿到某个字符并且拼接
            char ch = str.charAt(new Random().nextInt(str.length()));
            sb.append(ch);
        }
        System.out.println(sb);
    }
}