Question

更新：应用@ user27158建议的改进（谢谢）后，当我运行程序时遇到了另一个问题。

会弹出错误，并从本质上阻止程序继续。在调查了这一点之后，我无法弄清问题所在。再一次，我是编程的新手，很可能只是想念一些完全简单的东西。

错误消息：

线程“主”中的异常java.lang.UnsupportedOperationException：不支持。在country.game.EuropeanCountries.EuropeanCountriesList（EuropeanCountries.java:17）在country.game.Main.main（Main.java:36）返回的Java：1 失败（总时间：12秒）

该错误发生在以下行：

List<String> euCountries = EuropeanCountries.EuropeanCountriesList();

主类：

package country.game;

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


public class Main {

    public static List<String> EuropeanCountriesList() {
        List<String> EuropeanCountries = new ArrayList<>();
        return EuropeanCountries;
    }



    public static void main(String[] args) {

        boolean Running = true;

        List<String> UsedCountries = new ArrayList<>();

        Scanner Reader = new Scanner(System.in);

        while(Running == true){



            System.out.println("Pick a Country: ");
            String UserChoice = Reader.next();




            List<String> euCountries = EuropeanCountries.EuropeanCountriesList();

            if(!euCountries.contains(UserChoice)){
                System.out.println("That is not a valid country");
            } else {
                if(UsedCountries.contains(UserChoice)) {
                    System.out.println("Sorry you have already used that country");
                } else {
                    System.out.println("Correct! That Country is in Europe!");
                    UsedCountries.add(UserChoice);
                }
            }
        }        
    }           
}

“欧洲”课

package country.game;

import java.util.Arrays;
import java.util.List;

public class Europe {

    private static final List<String> EuropeanCountries = Arrays.asList(
            new String[]{
                "Albania",
                "Andorra",
                "Austria",

                "Belarus",
                "Belgium",
                "Bosnia and Herzegovina",
                "Bulgaria",

                "Croatia",
                "Czechia",

                "Denmark",

                "England",
                "Estonia",

                "Finland",
                "France",

                "Germany",
                "Greece",

                "Hungary",

                "Iceland",
                "Ireland",               
                "Italy",

                "Kosovo",

                "Latvia",
                "Liechtenstein",
                "Lithuania",
                "Luxembourg",

                "Malta",
                "Moldova",
                "Monaco",
                "Montenegro",

                "Netherlands",
                "Northern Ireland",
                "North Macedonia",
                "Norway",

                "Poland",
                "Portugal",

                "Romania",

                "San Marino",
                "Scotland",
                "Serbia",
                "Slovakia",
                "Slovenia",
                "Spain",
                "Sweden",
                "Switzerland",

                "Turkey",

                "Ukraine",

                "Vatican City",

                "West Russia",
            }
    );


    public static List<String> EuropeanCountriesList(){

    return EuropeanCountries;
    }    

}

任何帮助将不胜感激！

Answer 1

首先，您应该对代码进行一些改进；

运行永远不会增加，因此while循环永远不会结束
您只需要将扫描仪初始化一次，因此可以在循环外进行
您正在尝试将String与int进行比较
您的列表“ UsedCountries”是通用的。这绝不是一个好主意，因为它不限制可以输入的类型，这意味着您可能会出现仅在运行时显示的错误。应该声明为List<String> UsedCountries = new ArrayList<>();
变量和方法名称应以小写字母开头 https://www.oracle.com/technetwork/java/codeconventions-135099.html

解决方法：如何从其他类访问数组列表

通过您的方法将其退回
在返回列表中工作

    public static List<String> EuropeanCountriesList() {
        // declaring as List as it is best to not tie yourself to a specific implementation
        List<String> EuropeanCountries = new ArrayList<>();
        ...
        return EuropeanCountries;
    }

然后

    String UserChoice = Reader.next()
    List<String> euCountries = EuropeanCountries.EuropeanCountriesList();
    ...

以上代码允许您在当前代码中使用arraylist。我会建议进一步改进

有了列表后，只需使用contains方法而不是for循环

    List<String> euCountries = EuropeanCountries.EuropeanCountriesList();
    // step 1 - check if it is one of the acceptable countries
    if (!euCountries.contains(UserChoice)) {
        System.out.println("That is not a valid country");
    } else {
        // step 2 - check if it has already been selected
        if (UsedCountries.contains(UserChoice)) {
            System.out.println("Sorry You Have Already Used That Country");
        } else {
            System.out.println("Correct! That Country is in Europe!");
            UsedCountries.add(UserChoice);
        }
    }

与其在每次调用该方法时都创建国家列表，不如声明一次并返回存储的列表

public class Europe {
    private static final List<String> EuropeanCountries = Arrays.asList(
        new String[]{
            "Albania", 
            "Andorra",
            ...
        }
    );

    public static List<String> EuropeanCountriesList() {
        return EuropeanCountries;
    }
}

希望这对您有帮助

如何获取用户输入并在不同类中的数组列表中搜索用户输入？

1 个答案: