请老师帮我分析一下代码 ，帮我详细解释一下

import java.util.Scanner;

public class VerifyRegistration {

public static void main(String[] args) {

String[] userNames = {"mrsoft", "mr", "miss", "Admin."};

System.out.println("欢迎进入明日学院注册页面");

boolean flag = true;

String names = null;

String userName;

do {

Scanner sc = new Scanner(System.in);

System.out.println("请输入用户名：");

userName = sc.nextLine();

for (int i = 0; i < userNames.length; i++) {

names += userNames[i];

if (userName.equals(userNames[i])) {

System.out.println("该用户名已存在！请重新输入……");

}

if (!names.contains(userName)) {

flag = false;

}

}

} while (flag);

Scanner in = new Scanner(System.in);

System.out.println("请输入密码：");

String password = in.nextLine();

System.out.println("当前用户的用户名：" + userName.trim() + "\n当前用户的密码：" + password);

in.close();

}

}