java - 我在扫描字符串时遇到问题

Question

我希望用户输入一个单词，以便我可以将其分配给String day。输出是

Exception in thread "main" java.lang.NullPointerException at DaysOfTheWeek.main(DaysOfTheWeek.java:15)

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，因此您得到一个空指针异常。您应该按照此处的说明进行操作 read in input from the console 。