Question

每次我尝试修复错误时，我都会执行以下操作，但错误导致错误。

给出以下5行和5列的数组，其中包含城市之间的距离：

请注意，城市名称不在数组中;数组包含仅限数字条目，它们给出了两者之间的距离由行和列表示的城市。

编写语句以初始化数组距离上面给出的里程数据。
编写语句以打印以下菜单，读入两个城市数字，打印两个城市之间的距离：

要确定城市之间的里程数，请输入数字以下列表中的两个城市： 1：奥尔巴尼4：纽约 2：波士顿5：费城 3：哈特福德

输入您的城市号码：

**测试案例：奥尔巴尼与纽约之间的距离＆amp;＆amp;哈特福德和费城之间的距离

public class DistanceofCities {

private static final String keyboard = null;

public static void main(String[] args) {

    int [][] distance = {
            {0, 171, 115, 141, 240},
            {171, 0, 103, 194, 333},
            {115, 103, 0, 120, 235},
            {141, 194, 120, 0, 104},
            {240, 333, 235, 104, 0}

    };

    int mileage;
    int first = -1, second = -1;

       System.out.println("To determine the mileage between cities, enter the \n");
       System.out.println("numbers of two cities from the following list:\n");
       System.out.println("      1:  Albany           4:  NY\n");
       System.out.println("      2:  Boston           5:  Phila\n");
       System.out.println("      3:  Hartford\n\n");
       System.out.println("Enter your city numbers ==> ");
       first = keyboard.nextInt();
       second = keyboard.nextInt();
       mileage = distance[first-1][second-1];
       System.out.println("The distance between your two cities is ");
    }
}

Answer 1

这是固定代码;说明如下：

import java.util.Scanner;

public class DistanceOfCities {

    public static void main(String[] args) {

        Scanner keyboardReader = new Scanner(System.in);

        int[][] distance = {
                {0, 171, 115, 141, 240},
                {171, 0, 103, 194, 333},
                {115, 103, 0, 120, 235},
                {141, 194, 120, 0, 104},
                {240, 333, 235, 104, 0}

        };

        int mileage;
        int first = -1, second = -1;

        System.out.println("To determine the mileage between cities, enter the \n");
        System.out.println("numbers of two cities from the following list:\n");
        System.out.println("      1:  Albany           4:  NY\n");
        System.out.println("      2:  Boston           5:  Phila\n");
        System.out.println("      3:  Hartford\n\n");
        System.out.println("Enter your city numbers ==> ");
        first = keyboardReader.nextInt();
        second = keyboardReader.nextInt();
        mileage = distance[first - 1][second - 1];
        System.out.println("The distance between your two cities is " + mileage + ".");

    }

}

基本上，要读取用户的键盘输入，您需要扫描仪对象：

// This creates the scanner:
Scanner keyboardReader = new Scanner(System.in);

您看到的错误可能是由于您尝试从 null 对象引用（即指向任何内容的指针）调用方法nextInt（）的事实：

// Here, you defined keyboard as being null:
private static final String keyboard = null;

// Then, your code attempts to call a method from no object:
first = keyboard.nextInt();

最后，不要忘记在最后得到的字符串中添加里程数：

// Add mileage:
 System.out.println("The distance between your two cities is " + mileage + ".");

Answer 2

看起来你最后没有打印里程。尝试将代码的最后一行更改为：

System.out.println("The distance between your two cities is "+mileage);

Answer 3

更改代码，

public static void main(String[] args) {

            int [][] distance = {
                    {0, 171, 115, 141, 240},
                    {171, 0, 103, 194, 333},
                    {115, 103, 0, 120, 235},
                    {141, 194, 120, 0, 104},
                    {240, 333, 235, 104, 0}

            };

            int mileage;
            int first = -1, second = -1;
            Scanner in = new Scanner(System.in);
               System.out.println("To determine the mileage between cities, enter the \n");
               System.out.println("numbers of two cities from the following list:\n");
               System.out.println("      1:  Albany           4:  NY\n");
               System.out.println("      2:  Boston           5:  Phila\n");
               System.out.println("      3:  Hartford\n\n");
               System.out.println("Enter your city numbers ==> ");
               first = in.nextInt();
               second = in.nextInt();
               mileage = distance[first-1][second-1];
               System.out.println("The distance between your two cities is "+mileage);
            }

Answer 4

使用应该定义keyboard.Use Scanner class。

试试这个 import java.util.Scanner;

public class DistanceofCities {



public static void main(String[] args) {

    int [][] distance = {
            {0, 171, 115, 141, 240},
            {171, 0, 103, 194, 333},
            {115, 103, 0, 120, 235},
            {141, 194, 120, 0, 104},
            {240, 333, 235, 104, 0}

    };

    int mileage;
    int first = -1, second = -1;
       Scanner keyboard= new Scanner(System.in);
       System.out.println("To determine the mileage between cities, enter the \n");
       System.out.println("numbers of two cities from the following list:\n");
       System.out.println("      1:  Albany           4:  NY\n");
       System.out.println("      2:  Boston           5:  Phila\n");
       System.out.println("      3:  Hartford\n\n");
       System.out.println("Enter your city numbers ==> ");
       first = keyboard.nextInt();
       second = keyboard.nextInt();
       mileage = distance[first-1][second-1];
       System.out.println("The distance between your two cities is "+ mileage);
    }
}

有人可以帮我修复这个Java代码吗？

4 个答案: