Java 输入不工作(初学者)

Question

出于某种原因，我的代码不接受最后一行“What would you like to order:”的输入

谁能告诉我这里的错误是什么？它正在正确编译和一切。我只是一个初学者，所以请用基本术语告诉我。

import java.util.Scanner;
import java.util.*;

class RestaurantMain {
    public static void main(String[] args)
    {

        //Create an array list
        ArrayList menu = new ArrayList();

        //Variables//
        int choice;
        int customerChoice;
        boolean trueFalse;
        int restart = 0;
        String choice2;
        String addItems = "";
        int menuCount = 0;
        int indexCount = 0;
        String item = "";

        //Import input device
        Scanner in = new Scanner(System.in);

        ArrayList theMenu = new ArrayList();

        System.out.println("Welcome to the Cooper's restaurant system!");
        System.out.println("How can I help?");
        System.out.println("");
        System.out.println("1. Customer System");
        System.out.println("2. Management System");
        System.out.println("");
        System.out.println("");
        System.out.print("Which option do you choose: ");
        choice = in.nextInt();

            if (choice == 1) {
                System.out.println("Our menu's are as follows:");
                System.out.println("");
                System.out.println("1. Drinks");
                System.out.println("2. Starters");
                System.out.println("3. Mains");
                System.out.println("4. Desserts");
                System.out.println("");
                System.out.println("Please note - You MUST order 5 items.");
                System.out.println("");
                System.out.print("What menu would you like to follow? ");
                customerChoice = in.nextInt();

                    if (customerChoice == 1) {
                        System.out.println("Drinks Menu");
                            System.out.println("Would you like to order? ");
                            choice2 = in.nextLine();
                                if (choice2 == "yes") {
                                    System.out.println("Please enter the amount of items you want to order: ");
                                    while (indexCount <= menuCount);
                                        System.out.println("Please enter your item: ");
                                        item = in.nextLine(); {
                                        theMenu.add(item);
                                    }
                                    }

                    }
                    if (customerChoice == 2) {
                        System.out.println("Starters Menu");
                    }
                    if (customerChoice == 3) {
                        System.out.println("Mains menu");
                    }
                    if (customerChoice == 4) {
                        System.out.println("Desserts Menu");
                    }

Answer 1

您需要在调用 in.nextInt() 的行之后立即调用 in.nextLine() 原因是仅要求下一个整数不会消耗输入中的整行，因此您需要通过调用 in.nextLine() 跳到输入中的下一个换行符>

customerChoice = in.nextInt();
in.nextLine();

每当您在调用不消耗整行的方法后需要换行时，几乎都必须执行此操作。考虑改用 BufferedReader 对象!

BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
int integer = Integer.parseInt(reader.readLine());

如果输入不能被解析为整数，这将抛出与 Scanner.nextInt() 相同的错误。

关于您对错误的评论，有一个:

while (indexCount <= menuCount);
System.out.println("Please enter your item: ");
item = in.nextLine(); {
 theMenu.add(item);
}

应该像下面这样:

while(indexCount <= menuCount){
    System.out.println("Please enter your item: ");
    item = in.nextLine();
    theMenu.add(item);
}

此外，这不是绝对必要的，但我建议您在实例化列表时声明 ArrayList 的通用类型，这样对 theMenu.get() 的进一步调用就不需要强制转换为字符串。

ArrayList<String> theMenu = new ArrayList<String>();

比较字符串时，确保使用 str.equals("string to compare with") 方法，而不是相等运算符 (==)。因此，例如，choice2 == "yes" 应该改为 choice2.equals("yes")。使用 equalsIgnoreCase 而不是 equals 会忽略大小写差异，这在这种情况下可能很有用。