我的数组不能接受空格，也不能检测数组何时为空

Question

我正在尝试制作一个基于控制台的待办事项列表。

import java.util.Scanner;

// Press Shift twice to open the Search Everywhere dialog and type `show whitespaces`,
// then press Enter. You can now see whitespace characters in your code.
public class Main {

    public static final Scanner terminal = new Scanner(System.in);

    public static void main(String[] args) {
        to_do toDo = new to_do(terminal);
        toDo.Menu_loop();
        terminal.close();
    }
}

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

public class to_do {
    
    private ArrayList <String> todo_list;
    public static Scanner keyboard;

    public to_do(Scanner scanner) {
        keyboard = scanner;
        todo_list = new ArrayList <String>();
    }

    public void Menu_loop() {
        System.out.println("Welcome to to_o list please select a command:");
        printMenu();

        String userOption = "-1";

        while (!userOption.equals("4")) {

            userOption = keyboard.next();

            switch (userOption) {
                case "1" -> {
                    show_list();
                    printMenu();
                }
                case "2" -> {
                    add_list();
                    printMenu();
                }
                case "3" -> {
                    remove_list();
                    printMenu();
                }
                case "4" -> printQuitMessage();
                default -> {
                    System.out.println();
                    System.out.println("Error non valid command");
                    printMenu();
                }
            }
        }
    }
    
    public void show_list() {

        if (todo_list == null) {

            System.out.println("empty please add something");

        } else {
            for (String i: todo_list) {
                System.out.println(i);
            }
        }
    }
    
    public void add_list() {
        System.out.println("\n please write what you want to add: ");
        String name = keyboard.next();
        todo_list.add(name);
        System.out.println("\n item: " + name + " added to list");
    }
    
    public void remove_list() {
        System.out.println("\nplease write what you want to erase: ");
        String name = keyboard.next();

        if (!todo_list.contains(name) || todo_list == null) {
            System.out.println("error: your task does not exist or your list is empty");
        } else {

            todo_list.remove(name);
            System.out.println("item: " + name + " removed from list");
        }

    }

    public void printMenu() {
        System.out.println();
        System.out.println("Enter 1 - check list");
        System.out.println("Enter 2 - add task");
        System.out.println("Enter 3 - remove task");
        System.out.println("Enter 4 - Quit");
        System.out.print("Choice:");
    }
    
    private void printQuitMessage() {
        System.out.println("Closing the program bye bye!");
    }
}

我的问题是函数

add_list

和

show_list

。 当我尝试检查列表中是否存在任何项目时，开头总是

null

。

它应该会收到一条消息说

Empty please add something

如下代码：

public void show_list() {

    if(todo_list == null) {
        System.out.println("empty please add something");
    } else {
        for(String i : todo_list) {
            System.out.println(i);
        }
    }
}

但是我得到这个：

正如您在两个菜单打印之间看到的那样，当列表为空时它应该有消息

另一个问题是当我尝试输入字符串时： “喂狗” 当我尝试只检查单词 feed 是否存储在

add_list

.

public void add_list() {
    System.out.println("\n please write what you want to add: ");
    String name = keyboard.next();
    todo_list.add(name);
    System.out.println("\n item: " + name + " added to list");
}

Welcome to to_o list please select a command:

Enter 1 - check list
Enter 2 - add task
Enter 3 - remove task
Enter 4 - Quit
Choice:2

 please write what you want to add: 
feed the dog

 item: feed added to list

Enter 1 - check list
Enter 2 - add task
Enter 3 - remove task
Enter 4 - Quit
Choice:
Error non valid command

Enter 1 - check list
Enter 2 - add task
Enter 3 - remove task
Enter 4 - Quit
Choice:
Error non valid command

Enter 1 - check list
Enter 2 - add task
Enter 3 - remove task
Enter 4 - Quit
Choice:1
feed

Enter 1 - check list
Enter 2 - add task
Enter 3 - remove task
Enter 4 - Quit
Choice:1
feed

Enter 1 - check list
Enter 2 - add task
Enter 3 - remove task
Enter 4 - Quit
Choice:2

 please write what you want to add: 
de

 item: de added to list

Enter 1 - check list
Enter 2 - add task
Enter 3 - remove task
Enter 4 - Quit
Choice:1
feed
de

Enter 1 - check list
Enter 2 - add task
Enter 3 - remove task
Enter 4 - Quit