java - 将用户创建的对象存储在 arrayList 中多次迭代

Question

我已经在互联网上搜索了我遇到的问题的答案，但似乎无法得到我正在寻找的答案，我有两个类，应用程序类和用户类，我提示用户输入要么是新用户，要么返回已在数组列表中的用户的结果，该数组列表被设置为保存用户对象。应用程序结束后，我希望数组列表继续容纳对象，以便在应用程序类中每次连续运行 main 方法时，我都可以引用 arrayList 进行交叉检查。

所以我的问题是，当 main 方法完成并再次运行它时，它是否会从头开始重新创建我的所有对象和 arrayList？

下面是我正在使用的两个类(class)。应用程序类第一，用户第二。

import java.util.ArrayList;
import java.util.Scanner;

public class Application{
    static Scanner in = new Scanner(System.in);


    public static void main(String[] args) {


    //Creating admin user object that will be able to access everything
        Users admin = new Users();
        Users result = null;


    //creating a new user that is not an admin
        System.out.println("Are you a new user?");
        String answer = null;
        answer = in.nextLine();

        if(answer.equalsIgnoreCase("YES") || answer.equalsIgnoreCase("Y")) {
            result = admin.addNewUser();
            result.addUsertoArrayList(result);
        }else {
            result.displayUsers(result.users);
        }
    }//End of Main Method.
}//End of Application Class

import java.util.ArrayList;

public class Users extends Application {

    private String username;
    private double biWeeklyIncome = 0;
    private String password;
    private String email;

// ArrayList to store all the objects of Type Users.
    ArrayList<Users> users = new ArrayList<Users>();



// Default Constructor.
    Users() {
    }

// Constructor that takes a string as a name parameter.
    public String name;

    Users(String name) {
        this.name = name;
    }

// Setter Methods.

// User name
    public void setUsername() {
        System.out.println("Enter the username that you wish to go by:\n Ex.      bigBoss45");
       username = in.nextLine();
    }

// Income
    public void setBiWeeklyIncome() {
        System.out.println("Enter your current bi-weekly income: \n Ex.   4500.00");

        try {
            biWeeklyIncome = Double.parseDouble(in.nextLine());
        } catch (NumberFormatException e) {
        // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

// Password
    public void setPassword() {
        System.out.println("Enter the password that you wish to access your account with:\n Ex. bigBoss45");


        password = in.nextLine();
    }

// Email
    public void setEmail() {
        System.out.println("Enter a valid email address: \n Ex. bigBoss45@gmail.com");

        email = in.nextLine();
    }

// Getter Methods

// User name
    public String getUsername() {
        return username;
    }

// Income
    public double getBiWeeklyIncome() {
        return biWeeklyIncome;
    }

// Password
    public String getPassword() {
        return password;
    }

// Email
    public String getEmail() {
        return email;
    }

// Method to create a new user
    public Users addNewUser() {
        String name = null;

        System.out.println("Enter the name of the new user\n Ex.John Smith");
        name = in.nextLine();
    // Creating the new
        Users newUser = new Users(name);

    // Setting the new users information
        newUser.setUsername();
        newUser.setPassword();
        newUser.setBiWeeklyIncome();
        newUser.setEmail();

    //adding the new user to the users arrayList

        displayUsers(users);

        return newUser;
}// end of addNewUser method.

//Method that is going to add a new user to the array List.
    public void addUsertoArrayList(Users nUser) {
        users.add(nUser);
    }

    public void displayUsers(ArrayList<Users> users) {
    // Printing out the user added to the array list for testing purposes.
        for (Users user : users) {
            System.out.println(user.getUsername());
        }
    }//End of displayUser method.


}

我是 Java 和所有面向对象的新手，因此非常感谢您的帮助，感谢您花时间查看我的代码!

Answer 1

每次运行像 java Application 这样的命令来运行程序时，您都会启动一个新的 java 进程。内存中的任何数据都不会从 Java 程序的任何先前执行中继承。

如果您想存储数据，使其在流程的多次执行中保持不变，您应该考虑将其外部化到文件或数据库等。