import java.util.Scanner;

public class UI {

  protected char[] message;

public void printMessage(String message){
  System.out.println(this.message);
 
}
public String readMessage(){
Scanner sc=new Scanner(System.in);
String s = sc.nextLine();
return s;
}
}
 


class UserLoginUI extends UI{
String user=new String("user");
String pass=new String("pass");
UserLoginUI st;

void login(){
System.out.println("请输入用户名和密码：");
if(user.equals(st.readMessage())){
System.out.println("登陆成功");
}else{
System.out.println("登陆失败");  
} 
}
}




class AdminLoginUI extends UI{
String Admin=new String("user");
String pass=new String("pass");
AdminLoginUI st;

void login(){
System.out.println("请输入用户名和密码：");
 
if(Admin.equals(st.readMessage())){
System.out.println("登陆成功");
}else{
System.out.println("登陆失败");  
} 
}


}
class TestMain {

public static void main(String[] args){
UserLoginUI user1 = new UserLoginUI();
user1.login();
AdminLoginUI admin=new AdminLoginUI();
admin.login();
}

}

------解决方案--------------------

下面是帮你改的程序，一般用户是user user登陆，管理员是admin admin登陆
UI类没有改，改了UserLoginUI和AdminLoginUI 还有测试类

对应package你改成自己的包就可以了
Java code


public class UserLoginUI extends UI{
    String user=new String("user");
    String pass=new String("pass");
//    UserLoginUI st;

    public void login(){
        System.out.println("请输入用户名");
        String inputUser=this.readMessage();
        System.out.println("请输入密码");
        String password=this.readMessage();
        if(user.equals(inputUser)&&pass.equals(password)){
            System.out.println("登陆成功");
        }else{
            System.out.println("登陆失败");
        }
    }
}