Question

我希望用户输入一个字，以便将其分配给String day。输出是

在DaysOfTheWeek.main（DaysOfTheWeek.java:15）的线程“main”java.lang.NullPointerException中的异常

import java.util.*;"
public class DaysOfTheWeek {

    static Scanner scan;

    public static void main(String[] args) {

        System.out.println("What day is it today?");
        String day = scan.next();
        int dayNumber = 0;

        switch (day.toLowerCase()) {
            case "sunday":
                dayNumber = 0;
                break;
            case "monday":
                    dayNumber = 1;
                break;
            case "tuesday":
                    dayNumber = 2;
                break;
            case "wednesday":
                    dayNumber = 3;
                break;
            case "thursday":
                    dayNumber = 4;
                break;
            case "friday":
                    dayNumber = 5;
                break;
            case "saturday":
                    dayNumber = 6;
                break;

        }//switch

    }//main

}//end public class

Answer 1

您没有初始化scan对象，因此您获得了空指针异常。您应该按照此处有关如何read in input from the console的说明进行操作。

Answer 2

您尚未初始化扫描仪。

此外，无需将此扫描仪用作静态扫描仪。最好在主方法中初始化扫描仪。

import java.util.*;
public class DaysOfTheWeek {

public static void main(String[] args) {



    System.out.println("What day is it today?");
    Scanner scan = new Scanner(System.in);
    String day = scan.next();
    int dayNumber = 0;

    switch (day.toLowerCase()) {
        case "sunday":
            dayNumber = 0;
            break;
        case "monday":
                dayNumber = 1;
            break;
        case "tuesday":
                dayNumber = 2;
            break;
        case "wednesday":
                dayNumber = 3;
            break;
        case "thursday":
                dayNumber = 4;
            break;
        case "friday":
                dayNumber = 5;
            break;
        case "saturday":
                dayNumber = 6;
            break;

    }//switch

请记住，如果你想使用像Scanner这样的任何对象，那就更好，更容易地使用它。

    import java.util.*;
public class DaysOfTheWeek {

public static void main(String[] args) {



    System.out.println("What day is it today?");
    String day = new Scanner(System.in).next();


    int dayNumber = 0;

    switch (day.toLowerCase()) {
        case "sunday":
            dayNumber = 0;
            break;
        case "monday":
                dayNumber = 1;
            break;
        case "tuesday":
                dayNumber = 2;
            break;
        case "wednesday":
                dayNumber = 3;
            break;
        case "thursday":
                dayNumber = 4;
            break;
        case "friday":
                dayNumber = 5;
            break;
        case "saturday":
                dayNumber = 6;
            break;

    }//switch

因此main方法中的这段代码也是如此。

String day = new Scanner(System.in).next();

我在扫描字符串时遇到问题

2 个答案: