Java继承代码循环异常求助：选择1无法调用Agent子类

我编写了包含Person父类、Agent和Customer子类的Java代码，运行时出现异常循环：未编写循环逻辑，但输入1尝试调用Agent子类时，程序陷入重复显示[1]AGENT/[2]CUSTOMER选项的死循环；输入2则可正常执行对应逻辑。已经排查5-7小时，实在找不到问题所在。

相关代码 #

Person父类代码

import java.io.FileWriter;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Scanner;
import java.util.ArrayList;
import java.util.List;

class Person 
{
protected String agentId = "20860132";
protected String password = "20020729" ;
protected String address;

public Person(String agentId,String password, String address) 
{
    this.agentId = agentId;
    this.password = password;
    this.address = address;
    Scanner input = new Scanner(System.in);
    System.out.println("[1]AGENT");
    System.out.println("[2]CUSTOMER");
    int choice = input.nextInt();

    // 问题出在这里：程序会反复输出上面两行选项
    if(choice == 1) 
    {
       Agent agent = new Agent("Niel", "diko alam", "umay");
    }   
    else if(choice == 2)
    {
        System.out.println("POTANGINA");
    }   
}
}

Agent和Customer子类代码

class Agent extends Person 
{

public Agent(String agentId, String password, String address) 
{
super(agentId, password, address);
Scanner input2 = new Scanner(System.in);
System.out.println("[LOGIN]");
System.out.print("ENTER AGENT ID:");
int id = input2.nextInt();
System.out.print("ENTER PASSWORD:");
int pass = input2.nextInt();
if(id == 20860132 && pass == 20020729)
{
    Scanner input = new Scanner(System.in);
    System.out.println("[1]ADD CAR");
    System.out.println("[2]SCHEDULE");
    System.out.println("[3]RECORDS");
    int choice2 = input.nextInt();

if(choice2 == 1)
 {   
    boolean stopFlag = false;
    do 
    {
        List<String>cars = new ArrayList<String>();
        System.out.println("[CARS]");
        cars.add("Tayota");
        cars.add("Hillux");
        cars.add("Bugatti");
        System.out.println(cars);
        System.out.println("Enter Car:");
        String car = input.nextLine();
        cars.add(car);
        System.out.println("Would you like to add more?");
        System.out.println("[1]YES");
        System.out.println("[2]NO");
        String choice3 = input.nextLine();
        addCar(cars);
        if(!choice3.equals(1))
        stopFlag = true;
    }while(!stopFlag);
 }
}
else 
{
    System.out.println("INCORRECT PLEASE TRY AGAIN.");
}
}

public void addCar(List<String> cars) 
{
    try 
    {
        FileWriter fw = new FileWriter("cars.txt", true);
        PrintWriter pw = new PrintWriter(fw);
        pw.println(cars);
        pw.close();
    }
    catch (IOException e) 
    {
        e.printStackTrace();
    }

}

public void schedule(String schedule) 
{
    try 
    {
    FileWriter fw = new FileWriter("schedule.txt", true);
    PrintWriter pw = new PrintWriter(fw);
    pw.println(schedule);
    pw.close();
    } 
    catch (IOException e) 
    {
    e.printStackTrace();
    }

}

public void records(String record) 
    {
     try
        {
        FileWriter fw = new FileWriter("records.txt", true);
        PrintWriter pw = new PrintWriter(fw);
        pw.println(record);
        pw.close();
        } 
        catch (IOException e) 
        {
        e.printStackTrace();
        }

    }

}

class Customer extends Person 
{
private String customerId;

public Customer(String agentId, String password, String address, String customerId) 
{
super(agentId, password, address);
this.customerId = customerId;
}

public void setCustomerId(String customerId) 
{
this.customerId = customerId;
}

public String getCustomerId() 
{
return customerId;
}

public void rentCar(String car) 
{

    try 
    {
    FileWriter fw = new FileWriter("cars.txt", true);
    PrintWriter pw = new PrintWriter(fw);
    pw.println(car);
    pw.close();
    } 
    catch (IOException e) 
    {
    e.printStackTrace();
    }
}

public void viewSchedule(String schedule) 
{
    try 
    {
    FileWriter fw = new FileWriter("schedule.txt", true);
    PrintWriter pw = new PrintWriter(fw);
    pw.println(schedule);
    pw.close();
    } 
    catch (IOException e) 
    {
    e.printStackTrace();
    }
}

public void extend(String record) 
{
    try 
    {
    FileWriter fw = new FileWriter("records.txt", true);
    PrintWriter pw = new PrintWriter(fw);
    pw.println(record);
    pw.close();
    } 
    catch (IOException e) 
    {
    e.printStackTrace();
    }
}
}

主方法代码

public class Finals 
{
    public static void main(String[] args) 
    {
       Person person = new Person("20860132", "h208f32", "San luis");
       Agent agent = new Agent("20860132", "h208f32", "San luis");
    }
}

问题根源分析 #

1. 无限递归循环的核心原因：
   Person构造器中执行new Agent(...)创建子类实例，但Agent继承自Person，创建Agent时必须先调用父类Person的构造器（super()）。这就形成了死循环：

   • 进入Person构造器 → 输入1 → 创建Agent → 调用Person构造器 → 再次显示选项 → 输入1 → 创建Agent → 无限重复此流程

2. 次要问题：

   • 主方法同时创建Person和Agent实例，导致程序启动就执行两次Person构造器的选择逻辑
   • Agent类中choice3.equals(1)是字符串与整数直接比较，永远返回false，会导致添加车辆的循环无法停止
   • 重复创建Scanner实例，容易引发输入缓冲异常

修复方案 #

1. 剥离构造器中的业务逻辑

构造器仅负责初始化属性，把用户选择逻辑从Person构造器中移除：

class Person 
{
protected String agentId = "20860132";
protected String password = "20020729" ;
protected String address;

public Person(String agentId,String password, String address) 
{
    this.agentId = agentId;
    this.password = password;
    this.address = address;
}
}

2. 把选择逻辑移到主方法中

由主方法负责接收用户输入，创建对应实例：

public class Finals 
{
    public static void main(String[] args) 
    {
        Scanner input = new Scanner(System.in);
        System.out.println("[1]AGENT");
        System.out.println("[2]CUSTOMER");
        int choice = input.nextInt();

        if(choice == 1) 
        {
           Agent agent = new Agent("20860132", "h208f32", "San luis");
        }   
        else if(choice == 2)
        {
            System.out.println("POTANGINA");
            // 此处可添加Customer实例创建逻辑
            // Customer customer = new Customer("xxx", "xxx", "xxx", "xxx");
        }
        input.close();
    }
}

3. 修复Agent类中的字符串比较问题

将字符串与整数的错误比较改为字符串间的比较，同时处理输入缓冲的换行符：

// 修改Agent类中添加车辆的循环部分
if(choice2 == 1)
 {   
    boolean stopFlag = false;
    do 
    {
        List<String>cars = new ArrayList<String>();
        System.out.println("[CARS]");
        cars.add("Tayota");
        cars.add("Hillux");
        cars.add("Bugatti");
        System.out.println(cars);
        System.out.println("Enter Car:");
        // 处理上一次nextInt()遗留的换行符
        input.nextLine();
        String car = input.nextLine();
        cars.add(car);
        System.out.println("Would you like to add more?");
        System.out.println("[1]YES");
        System.out.println("[2]NO");
        String choice3 = input.nextLine();
        addCar(cars);
        // 改为字符串比较
        if(choice3.equals("2"))
            stopFlag = true;
    }while(!stopFlag);
 }

4. 统一使用单个Scanner实例

避免重复创建Scanner，减少输入异常风险。

内容的提问来源于stack exchange，提问作者newbie