java如何在两个不同的方法中使用相同的变量，而不使这些变量成为全局变量？

Question

我的简单程序将要求用户输入几个城市。用户应该能够通过选择其他选项打印出来

现在我在一个方法（city();）中声明了一个数组来存储这些值。我有两种不同的方法，分别询问用户和打印出（这将在主类中调用）。如果我想在printCity()method中打印数组（），它必须使用另一个方法（city();）中使用的变量。因此，printCity()方法显示了找不到变量的错误。此外，在我的情况下（I不知道为什么）将这些变量声明为全局（在方法之外）不起作用。 那么，我如何解决这个问题，使相同的变量在两种不同的方法中工作

我的代码： 主要类别：

    package city;

import java.util.*;

public class City {

    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        UserInput ui = new UserInput();

        System.out.println("                THIS PROGRAM WILL TELL YOU THE CITY YOU HAVE EVER TRAVELLED\n"
                + "                          Choose one of the following option\n\n"
                + "                           You must enter city name before printing them out!");

        System.out.println("1. Enter the cities you have travelled\n"
                + "2. Print out the cities\n"
                + "3. Exit\n"
                + "....................\n"
                + "....................");

        while (true) {

            int userChoose = input.nextInt();

            switch (userChoose) {

                case 1:
                    //call method where the program asks to enter city name
                    ui.city();
                    break;
                case 2:
                    //call method where the program prints out the city name   

                    ui.printCity();
                    break;
                case 3:
                    System.exit(0);
                default:
                    System.out.println("Invalid input! Plz try again: ");
            }

        }

    }

}

用户输入类：

    package city;

import java.util.*;

public class UserInput {

    Scanner inScanner = new Scanner(System.in);

    public void city() {
        System.out.println("How many favourite city you have in your list?");
          int numOfCity = inScanner.nextInt();
        String[] cityInArr = new String[numOfCity];

        for (int i = 0; i < numOfCity; i++) {
            System.out.println("City " + (i + 1) + ": ");
            cityInArr[i] = inScanner.next();

        }
        System.out.println("YOU ARE DONE! NOW PRINT THEM OUT");

    }

    public void printCity() {


        System.out.println("");
        System.out.println("These are your favorite cities: ");
        for (int j = 0; j < numOfCity; j++) {//has an error
            System.out.printf("%s ", cityInArr);//has an error

        }


    }
}

Answer 1

听起来city()方法应该返回城市数组，然后可以将其传递给printCity()方法：

public String[] city() {
    ...
    return cityInArr;
}

public void printCity(String[] cities) {
    ...
}

在你的电话号码中：

String[] cities = {}; // Empty until fetched

...
cities = ui.city();
...
ui.printCity(cities);

我也强烈建议你重新考虑你的名字。例如，IMO认为getFavoriteCities()和displayCities()更合适

Answer 2

您需要将它作为方法参数传递

public void printCity(String[] cityInArr, int numOfCity) {


        System.out.println("");
        System.out.println("These are your favorite cities: ");
        for (int j = 0; j < numOfCity; j++) {//has an error
            System.out.printf("%s ", cityInArr);//has an error

        }

那就这样说吧

   public static void main(String[] args) {
     .......
     printCity(cityArray, numOfCity);
     ........
    }

Answer 3

假设“global”指的是将它们声明为UserInput类的字段（如果你指的是其他内容，请纠正我），我无法理解你为什么不想这么做

考虑到您在同一类的同一实例的两个方法之间共享数据，一个字段正是您所需要的

我冒昧地重写了UserInput类，将数组作为字段（主类的工作方式不变）。还要注意的是，你不需要传递城市的数量，因为它是由数组的长度决定的

public class UserInput {
    private String[] cityInArr;

    public void city() {
        System.out.println("How many favourite city you have in your list?");
        Scanner inScanner = new Scanner(System.in);
        int numOfCity = inScanner.nextInt();
        cityInArr = new String[numOfCity];

        for (int i = 0; i < numOfCity; i++) {
            System.out.println("City " + (i + 1) + ": ");
            cityInArr[i] = inScanner.next();
        }
        System.out.println("YOU ARE DONE! NOW PRINT THEM OUT");
    }

    public void printCity() {
        System.out.println("\nThese are your favorite cities: ");
        for (int j = 0; j < cityInArr.length; j++) {//has an error
            System.out.printf("%s ", cityInArr[j]);//has an error
        }
    }
}