Question

我的问题是尝试读取包含不规则数组的文件。我想我差不多了，但我一直得到一个空指针异常错误。欢迎任何帮助或建议。这是我的代码。

    import java.io.*;
    import java.util.Scanner;
    import java.util.*;
    public class Calories2{
    public static void fileReaderMethod(String fileName) throws FileNotFoundException, IOException {// This method reads the file and inputs the measurements 
        Scanner input ;
        try{                                                                                            // into an array of type int.
            input = new Scanner (new File(fileName));
            }
            catch (FileNotFoundException e){
                System.out.println("File Does Not Exist");
                System.out.println("Choose another file");
                Scanner in = new Scanner(System.in);
                fileName = in.next();
                input = new Scanner (new File(fileName));
            }

            FileReader fr = new FileReader(fileName);
            BufferedReader textReader = new BufferedReader(fr);
            int row=0;
            String currentRow;
            while((currentRow = textReader.readLine())!= null){
                rows++;
            }
            fr = new FileReader(fileName);
            textReader = new BufferedReader(fr);
            String [] columns = textReader.readLine().split(" ");

            int [][] caloriesOfTheWeekArray = new int [7][];
            fr = new FileReader(fileName);
            textReader = new BufferedReader(fr);

            for(int i = 0; i < caloriesOfTheWeekArray.length; i++){
                String columnArray [] = textReader.readLine().split(" ");
                for (int j = 0; j < columns.length; j++){
                    caloriesOfTheWeekArray[i][j] = Integer.parseInt(columnArray[j]);
                }
            }
}
public static void main (String [] args)throws FileNotFoundException, IOException {
    fileReaderMethod("Calories.txt");
}
    }

这是我得到的错误。

    Exception in thread "main" java.lang.NullPointerException
    at Calories2.fileReaderMethod(Calories2.java:36)
    at Calories2.main(Calories2.java:41)

第36行

    caloriesOfTheWeekArray[i][j] = Integer.parseInt(columnArray[j]);

和41是我调用读取文件的方法

文件我正在尝试阅读

    200 10000
    450 845 1200 800
    800
    400 1500 1800 200
    500 1000
    700 1400 170
    675 400 100 400 300

Answer 1

问题在于您对caloriesOfTheWeekArray，

使用的初始化类型

 int [][] caloriesOfTheWeekArray = new int [7][];

这将初始化7行但无法初始化您的列，因为您尚未指定它们。如果没有初始化您的列，您将尝试访问第36行中的列

 caloriesOfTheWeekArray[i][j] = Integer.parseInt(columnArray[j]);

这导致你的NPE。

因此请将长度为columnArray.length的列初始化。

 for(int i = 0; i < caloriesOfTheWeekArray.length; i++){
            String columnArray [] = textReader.readLine().split(" ");
            caloriesOfTheWeekArray[i] = new int[columnArray.length];
            for (int j = 0; j < columnArray.length; j++){
                caloriesOfTheWeekArray[i][j] = Integer.parseInt(columnArray[j]);
            }
        }

此外，您使用column.length代替columnArray.length，而{i}也负责NPE。

将文件读入Ragged Array

1 个答案: