卡在 Java 中的 2 个 NullPointerException 错误

Question

我正在尝试将文件列表加载到数组中，然后获取这些数组并从中逐行提取信息。我已经尝试解决这个问题将近 4 个小时了，但我不明白 NullPointerException 错误要我做什么。我在 initializeLocations 方法中的 for 循环声明处以及调用 burns.initializeLocations() 时的主要错误中收到错误。有什么建议么？

import java.io.File;
import java.io.IOException;
import org.apache.commons.io.FileUtils;

public class LocationNode
{
   private String name;
   private String hoursText;
   private String descriptionText;
   //add image for location for info page as an attribute later

public LocationNode(){
    name = "";
    hoursText = "";
    descriptionText = "";
}

//constructor
public LocationNode(String initName, String initHours, String initDescription){
    name = initName;
    hoursText = initHours;
    descriptionText = initDescription;
}

public void setName(String textName){
    name = textName;
}

public String getName(){
    return name;
}

public void setHours(String textHours){
    hoursText = textHours;
}

public String getHours(){
    return hoursText;
}

public void setDescription(String textDescription){
    descriptionText = textDescription;
}

public String getDescription(){
    return descriptionText;
}

public void initializeLocations() throws IOException
{
    File folder = null;
    File[] listOfFiles;

    //creates "path to files" variable
    folder = new File(".Tiger Map App/src/LocationTextFiles"); 

    //creates array of all the files in the folder
    listOfFiles = folder.listFiles(); 

    for (int i = 0; i < listOfFiles.length; i++) { //runs for loop to "number of files"
        //takes current file in loop iteration and sticks it in a temp file
        File temp = listOfFiles[i]; 
        //checks if file is valid
        if (temp.isFile() && temp.getName().endsWith(".txt")) 
        {
            //takes contents of file and places them into a String(can replace "content" variable w/ array)
            String content = FileUtils.readFileToString(temp, "UTF-8"); 

            //test printing if contents are actually pulling from file
            System.out.println(content); 
        }
    }       
}

public static void main(String[] args) throws IOException
{
    LocationNode burns = new LocationNode();
    burns.initializeLocations();
}

}

Answer 1

//creates "path to files" variable
folder = new File(".Tiger Map App/src/LocationTextFiles"); 

//creates array of all the files in the folder
listOfFiles = folder.listFiles();

您确定这是正确的目录吗？如果该目录中没有文件或者您指定的目录名称不正确，我在此处复制的第二行可以将 listOfFiles 分配给 null。然后在你的循环中

listOfFiles.length

将导致空指针，因为您正在尝试获取空实例的长度。

Answer 2

根据the documentation，“.Tiger Map App/src/LocationTextFiles”很可能不是文件夹。

Returns null if this abstract pathname does not denote a directory, or if an I/O error occurs.

Answer 3

listOfFiles 可以为空。检查这是正确的 folder = new File(".Tiger Map App/src/LocationTextFiles"); 在循环之前输出 listofffiles 的值，我怀疑它将为空，因此 listoffiles.length 抛出异常。

卡在 Java 中的 2 个 NullPointerException 错误

Stuck on 2 NullPointerException errors in Java

java

file-io

android

nullpointerexception