Program to get all files within a directory in Java

Question

I'm working on this program to get all the files in the directory. For some reason I am getting a NullPointerException on Line 16. I don't know why though since this is a template that seemed to work in class with our teacher. Thanks.

import java.util.*;
import java.io.*;

public class FindDirectories {
    public static void main(String[] args) { 
        if (args.length == 0) { 
            args = new String[] { ".." }; 
        }

        List<String> nextDir = new ArrayList<String>(); 
        nextDir.add(args[0]); // either the one file, or the directory
        try { 
            while(nextDir.size() > 0) {     // size() is num of elements in List 
                File pathName = new File(nextDir.get(0)); // gets the element at the index of the List 
                String[] fileNames = pathName.list();  // lists all files in the directory
                for(int i = 0; i < fileNames.length; i++) { 
                  File f = new File(pathName.getPath(), fileNames[i]); // getPath converts abstract path to path in String, 
                                                                    // constructor creates new File object with fileName name   
                  if (f.isDirectory()) { 
                     System.out.println(f.getCanonicalPath()); 
                     nextDir.add(f.getPath()); 
                  } 
                  else {
                      System.out.println(f);
                  }
               } 
               nextDir.remove(0); 
            } 
        } 
        catch(IOException e) { 
            e.printStackTrace();  
        }       
    } 
}

krock · Accepted Answer · 2013-08-03T22:58:24.207

9

Check out the Javadoc for File.list(). Specifically:

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

In your code pathName.list(); must be returning null so pathName does not represent a valid directory, or an IO error occurred trying to get a list of files from that directory.

edited Aug 03 '13 at 22:58

answered Jul 26 '10 at 06:03

krock

28,904
13
79
85

how do i check it? do i just say pathName.list() != null? – Crystal Jul 30 '10 at 06:21
Yes @Crystal, you should test for that. Then decide what to do when this happens: report error, prompt user for correct dir etc. – krock Jul 30 '10 at 10:19

score 4 · Answer 2 · edited Oct 27 '12 at 00:19

Use bellow snippet to get all the files from all the sub directories:

import java.io.File;

/**
 *
 * @author santoshk
 */
public class ListFiles {

     File mainFolder = new File("F:\\personal");
     public static void main(String[] args)
     {
         ListFiles lf = new ListFiles();
         lf.getFiles(lf.mainFolder);
     }
     public void getFiles(File f){
         File files[];
         if(f.isFile())
             System.out.println(f.getAbsolutePath());
         else{
             files = f.listFiles();
             for (int i = 0; i < files.length; i++) {
                 getFiles(files[i]);
             }
         }
     }
}

score 0 · Answer 3 · edited Sep 08 '14 at 17:53

0

import java.io.*;

public class filedir 
{
    public static void main(String[] args)
    {
        try{
            Files f = new File("C:\\");//the path required
            String a[];
            a=f.list(); 
            for (int i = 0; i <a.length; i++) {
               System.out.println(a[i]);
              }
        } catch(Exception e) {
            System.err.println(e);
        }
    }
}

edited Sep 08 '14 at 17:53

Dennis

3,683
1
21
43

answered Jan 23 '13 at 19:18

anjuna

1

1

I hope u get the idea with this small code...sorry if it was not the answer to the question. – anjuna Jan 23 '13 at 19:20

score 0 · Answer 4 · answered Jul 26 '10 at 06:05

If you're getting a NullPointerException on line 16, it must mean that fileNames is null, so fileNames.length is invalid. Take a look at the javadoc for File.list and you'll see that pathName.list() can be null if pathName is not a directory, or if an exception occurs. So you'll just need to check whether fileNames is null before trying to use it.

score 0 · Answer 5 · edited Apr 23 '11 at 10:42

import java.io.File;
import java.util.ArrayList;
import java.util.LinkedList;


public class FileEnumerator {

    /**
     * @param args
     * @throws IOException 
     */
    public static void main(String[] args) throws IOException {

        // Prepare the List of files
        String path = "C:/";
        ArrayList<String> Files = new ArrayList<String>();
        LinkedList<String> Dir = new LinkedList<String>();
        File f = new File(path);
        Dir.add(f.getAbsolutePath());
        while(!Dir.isEmpty())
        {
            f = new File(Dir.pop());
            if(f.isFile())
            {
                Files.add(f.getAbsolutePath());
            }
            else
            {
                String arr[] = f.list();
                try
                {
                for(int i = 0;i<arr.length;i++)
                {
                    Dir.add(f.getAbsolutePath()+"/"+arr[i]);
                }
                }
                catch(NullPointerException exp)
                {
                    Dir.remove(f.getAbsoluteFile());
                }
            }
        }


                //Print the files
        for(int i = 0;i<Files.size();i++)
        {
            System.out.println(Files.get(i));
        }
    }

}

I think this code should work well. Although I have tested it just on Windows. But other OS will need at most small changes.

"I think this code should work well. Although I have tested it just on Windows. But other OS will need at most small changes." Given that good Java code should run on other OS with **no** changes, the code in your answer is *not* a good example. At the very least it should use either `System.getProperty("file.separator")` or the `File` constructor that accepts path/name arguments instead of `/`. Then we might go into using `String` objects to represent `File`s. Presuming a `C:` drive rather than accepting a command line arg. (...) — Andrew Thompson, Apr 23 '11 at 10:48

Program to get all files within a directory in Java

5 Answers5

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