Java 将患者信息存储到文本文件中，然后加载

我们的任务是编写一个简单的医院管理系统。用户可以输入患者信息，如姓名、性别、出生日期和疾病
数据存储在ArrayList中，并保存到文本文件中

现在我的问题是：我需要显示输入系统的所有患者
但我无法以正确的方式获取数据并将其显示在控制台窗口中
输出内容应为：患者姓名、性别、疾病、出生日期

这是我的。。它不是全部代码，只是部分代码。
这是主课

import java.io.*;
import java.util.*;

public class Main {

public static void main (String args []) {

    int choice = 0;

    List<Patient> PatientList = new ArrayList<Patient>();       
    Patient patient = new Patient();        
    List<Doctor> DoctorList = new ArrayList<Doctor>();
    Doctor doctor = new Doctor();

    Scanner readInput = new Scanner(System.in);
    Scanner readChoice = new Scanner(System.in);        


    do {
            System.out.println("Press 1 to enter a new patient \nPress 2 to enter a new doctor \nPress 3 to show all patients \nPress 4 to show all doctors \nPress 0 to quit.");   
            choice = readChoice.nextInt();

        switch (choice) {

            //case 0: 

            case 1: System.out.println("Please enter the name of the new patient: ");
                    patient.setPatientName(readInput.nextLine());


                    System.out.println("Please enter the gender of the new patient: ");
                    patient.setPatientGender(readInput.nextLine());

                    System.out.println("Please enter the disease of the new patient: ");
                    patient.setDisease(readInput.nextLine());       

                    System.out.println("Please enter the age of the new patient: ");
                    patient.setPatientDateOfBirth(readInput.nextLine());

                    PatientList.add(patient);

            try {
                FileOutputStream fos = new FileOutputStream("patients.tmp");
                ObjectOutputStream oos = new ObjectOutputStream(fos);
                oos.writeObject(PatientList);
                oos.close();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

                    break;      

/////////////////////////////////////////////////////////////////   
//case 2 is not relevant to my question therefore I did not put it in here

            case 3: if(PatientList.size() == 0) {

                        System.out.println("\nNo patients were found...\nReturning to main menu...\n");     

                    } 

                    else {  


                            try {
                                FileInputStream fis = new FileInputStream("patients.tmp");
                                ObjectInputStream ois = new ObjectInputStream(fis);
                                PatientList =(ArrayList<Patient>) ois.readObject();
                                ois.close();
                                fis.close();
                            } catch (FileNotFoundException e) {
                                // TODO Auto-generated catch block
                                e.printStackTrace();
                            } catch (ClassNotFoundException e) {
                                // TODO Auto-generated catch block
                                e.printStackTrace();
                            } catch (IOException e) {
                                // TODO Auto-generated catch block
                                e.printStackTrace();
                            }


                        for (int i = 0; i < PatientList.size(); i++) {                              

                            System.out.println(PatientList.get(i).getPatientName()+", "+PatientList.get(i).getPatientDateOfBirth()+", "
                            +PatientList.get(i).getPatientGender()+", "+PatientList.get(i).getDisease());                       

                        }

                    }                       
                    break;

我猜在主课（案例3）中有一些错误，但我自己解决不了

---

我非常感谢你的帮助

它在第一次启动时从不从磁盘加载数据的原因是，案例3中的第一个if语句检查PatientList.size是否为空，如果为空，则不从磁盘加载数据（else语句仅在列表中有问题时运行）

要解决这个问题，您可能需要检查PatientList.isEmpty（）是否正确，如果正确，则尝试从磁盘加载数据，如果没有数据，则打印出未找到的记录

case 3: 
    if(PatientList.isEmpty()) 
    {
        try 
        {
            //load data from the hard drive
        } catch (FileNotFoundException e) {
        } catch (ClassNotFoundException e) {
        } catch (IOException e) {
        }

        //populate PatientList if data was loaded from disk here

        //if PatientList is still empty then print out no patients found
        if(PatientList.isEmpty())
        {
            System.out.println("\nNo patients were found...\nReturning to main menu...\n");
        }           
    }

break;

---

您得到的输出是什么（与预期输出进行比较）？在案例3中，您应该检查`if（PatientList.isEmpty（））{}`这可能无法解决您的问题，但这只是使用collection时应该编写的内容之一。另外，最好使用try with resources或使用finally块来关闭流。如果PatientList.size（），则只能从磁盘加载数据0是有意的吗？我想这是检查列表中是否有可以加载的内容的方法。我删除了if/else语句，现在可以加载数据了。有人能给我解释一下吗？我应该使用if（PatientList.isEmpty（））吗？好吧，我想我知道问题出在哪里了。。当程序启动时，数组将始终为空，因为到目前为止没有加载任何数据。是吗？@r4ZR2810我发布的修复代码中有一个小错误。现在它已经被修复了。我几乎尝试了所有的方法将文件读入ArrayList，但是我没有注意到我在if语句中犯的错误。谢谢！

case 3: 
    //this if statment is checking if PatientList.size() is 0 or in other words check if it is empty
    if(PatientList.size() == 0) 
    {
        System.out.println("\nNo patients were found...\nReturning to main menu...\n");     
    }
    //this else code block will only run if the above if statment is false
    else 
    {  
        try 
        {
            //load data from the hard drive
        } catch (FileNotFoundException e) {
        } catch (ClassNotFoundException e) {
        } catch (IOException e) {
        }
    }                       
break;

case 3: 
    if(PatientList.isEmpty()) 
    {
        try 
        {
            //load data from the hard drive
        } catch (FileNotFoundException e) {
        } catch (ClassNotFoundException e) {
        } catch (IOException e) {
        }

        //populate PatientList if data was loaded from disk here

        //if PatientList is still empty then print out no patients found
        if(PatientList.isEmpty())
        {
            System.out.println("\nNo patients were found...\nReturning to main menu...\n");
        }           
    }

break;