java - 将 ArrayList 从一个类传递到另一个类

Question

我对 Java 比较陌生，所以如果我犯了任何明显的错误，我深表歉意。我试图将 ArrayList“数字”从“IO”类传递到“交互”类。我正在尝试将数字的内容打印到控制台作为测试。当我调用 getNumbers 方法时，控制台保持为空。我究竟做错了什么？这是我所拥有的:

IO 类:

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

public class IO {
    public static void main (String[] args){
        fileInput();
    }
    public static void fileInput() {
        //variable setup
        String file = "src/seats.txt";
        int number;

        ArrayList<Integer> numbers = new ArrayList<Integer>();


        //Read file into the ArrayLists
        try {
            Scanner input = new Scanner(new FileReader(file));

            while (input.hasNextLine()){    //read a line from file
                number = input.nextInt();
                input.nextLine();

                numbers.add(number);
            }
            input.close();
        }
        catch (IOException e){
            System.out.println(e);
        }
        public static ArrayList<Integer> getNumbers(){
            ArrayList<Integer> numbers = new ArrayList<Integer>();
            return numbers;
        }
    }

交互类:

import java.io.*;
import java.util.ArrayList;
import java.util.Scanner;
public class Interaction {

    public static void main(String[] args) {
        menu();
        IO.fileInput();
    }
    static Scanner consoleInput = new Scanner (System.in);
    public static void menu (){
        String userChoice = "";

        while (!userChoice.equals("QUIT")){
            System.out.println("|            MAIN MENU              |");
            System.out.println("|-----------------------------------|");
            System.out.println("|                                   |");
            System.out.println("| 1.) Reserve a Seat                |");
            System.out.println("| 2.) Cancel a Reservation          |");
            System.out.println("| 3.) View Waiting List             |");
            System.out.println("| Quit.) Exit Program               |");
            System.out.println("|                              v0.1 |");
            System.out.println("\nPlease make your selection:");

            userChoice = consoleInput.next().toUpperCase();

            switch(userChoice){
                default:
                if (!userChoice.equals("1") && !userChoice.equals("2") && !userChoice.equals("3")){
                System.out.println("Invalid option, please try again.");
            }
            pause();
            break;
            case "1":
            if (userChoice.equals("1")){
                reserveSeat();
            }
            pause();
            break;
            case "2":
            if(userChoice.equals("2")){
                getNumbers();
                cancel();
            }
            pause();
            break;
            case "3":
            if(userChoice.equals("3")){
                waitingList();
            }
            pause();
            break;
            case "QUIT":
            System.out.println("Thank you for using our service!");
            consoleInput.close();
            }
        }
     }

    private static void reserveSeat() {
        String type, direction, userChoice = null;
        int number;

    private static void cancel() {
        System.out.println("Test 2");
    }
    private static void waitingList() {
        System.out.println("Test 3");
    }
    private static void pause(){
        System.out.println("Press enter to return to the menu.");
        Scanner enter = new Scanner(System.in);
        enter.nextLine();
    }
    public static void getNumbers(){
        ArrayList<Integer> numbers = IO.getNumbers();
        System.out.println();
        int sz = numbers.size();
        for (int i = 0; i < sz; i++){
            System.out.println(numbers.get(i).toString());
        }
    }
}

我知道以前也有人问过类似的问题，但我找不到任何特别有用的东西。任何帮助将不胜感激。

编辑:现在显示整个 Interaction 类，而不仅仅是 getNumbers()

Answer 1

您希望相同的数字在IO.fileInput()和IO.getNumbers()中可见>;您可以添加一个类(static)numbers 字段，并在两个地方使用it(并编程到List) > 接口(interface))。类似的东西

private static List<Integer> numbers = new ArrayList<>();
public static List<Integer> getNumbers(){
    return numbers;
}

然后，不要忘记从 fileInput 中删除 numbers 声明(以便它使用 static 字段)。