时间戳

首页 > 解决方案 > 我的开关案例中的空指针异常错误

java - 我的开关案例中的空指针异常错误

问题描述

这是一个使用散列图的简单程序，它利用一个排名系统，从一个名为“babynameranking2008.txt”的文件中为男婴和女婴命名。我在我的变量排名的 switch case 中收到一个空指针异常，

该错误仅发生在男孩和女孩的每个开关案例的变量中，例如：“ranking=boys[index].get(name);”。如果我使排名等于 0，它将删除异常。

public class Lab08 {
    @SuppressWarnings("unchecked")
    private static Map<String, Integer>[] boys = new HashMap[10];
    @SuppressWarnings("unchecked")
    private static Map<String, Integer>[] girls = new HashMap[10];

    public static void main(String[] args) throws IOException {
        Scanner input = new Scanner(System.in);
        String answer;
        readNames(); // method to read the info from the files and add to our Map array                     
        // Get user input and continue until done

        do {
            System.out.print("ENter a year (2008-2017): ");
            int year = input.nextInt();input.nextLine();
            System.out.print("Boy or girl? ");
            String sex = input.nextLine().toLowerCase();
            System.out.print("ENter a name: ");
            String name = input.nextLine();

            sex = sex.toLowerCase();
            int index = 0;
            int ranking = 0;
            switch (sex) {
                // display the output based on the sex (boy or girl)
                case "boy":
                   index = year - 2008;
                   ranking = boys[index].get(name);
                   System.out.printf("The Boy named %s is ranked %d in %d \n",name,ranking,year);                  
                   break;

                case "girl":
                   index=year-2008;
                   ranking=girls[index].get(name);
                   System.out.printf("The Boy named %s is ranked %d in %d \n",name,ranking,year);
                   break;

                default:
                   System.out.println("sex should be boy or girl");
                   break;
            }
            //input.close();
            System.out.print("Do you want check another name (yes or no)?");
            answer = input.nextLine().toLowerCase();
        } while (answer.equals("yes"));
    } // end main

    //read information from each file and add to appropriate Map array
    public static void readNames() throws IOException {
        String fixedName="babynameranking";
        int year=2008;
        String type=".txt";

        File infile;
        for(int i=0;i<10;++i) {
            boys[i] = new HashMap<>();
            girls[i] = new HashMap<>();             
        }           

            for(int i=0;i<=9;++i) {
              // construct the file name
            String filename = fixedName+Integer.toString(year)+type;// construct the file name ;
            infile = new File(filename);

            Scanner in = new Scanner(infile);
            while(in.hasNext()) {
                // read info from the file and add to Map arrays
                int ranking=in.nextInt();
                   String boyName=in.next();
                   in.next();

                   String girlName=in.next();
                   in.next();

                 //put in map
                   boys[i].put(boyName, ranking);
                   girls[i].put(girlName, ranking);

            } // end while
            in.close();

            year=year+1;

        } // end for loop
    } // end readNames()

} // 结束 Lab08

标签： javanullpointerexception

解决方案

问题是您没有包含文件的路径。因此，抛出FileNotFoundException 。

在此处插入文件的路径：

 String filename = fixedName + Integer.toString(year) + type;

将其更改为如下所示：

String filename="/Users/../Desktop/babynameranking.txt";

而且你也不需要这些变量：

String fixedName="babynameranking";
int year=2008;
String type=".txt";

推荐阅读