Java File List: NPE while using for loop

Question

I've written simple java code to display file list in Linux to use it for FTP program using TCP(I'm going step by step, using all features). I'm posting this question after googling for about half an hour.

import java.io.*;
class FileList
{
public static void main(String args[])
{
String dirname="/home/vaibhav/Test";
File f1=new File(dirname);
String sl[]=f1.list();
System.out.print(f1.list()+"......."+sl.length+" files found.");
for(int i=0;i<sl.length;i++)
{ 
System.out.print(sl[i]+" ");
}      
}
}

Output:

vaibhav@vaibhav-VirtualBox:~/Java$ javac FileList.java
vaibhav@vaibhav-VirtualBox:~/Java$ java FileList
Exception in thread "main" java.lang.NullPointerException
    at FileList.main(FileList.java:10)

My Directories Test and Java contents:

vaibhav@vaibhav-VirtualBox:~$ cd /home/vaibhav/Test
vaibhav@vaibhav-VirtualBox:~/Test$ dir
1  2
vaibhav@vaibhav-VirtualBox:~/Test$ ls -al
total 8
drwxrwxrwx  2 vaibhav vaibhav 4096 Jan 18 15:04 .
drwxr-xr-x 25 vaibhav vaibhav 4096 Jan 18 16:50 ..
-rw-rw-rw-  1 vaibhav vaibhav    0 Jan 18 15:04 1
-rw-rw-rw-  1 vaibhav vaibhav    0 Jan 18 15:04 2
vaibhav@vaibhav-VirtualBox:~/Test$ cd
vaibhav@vaibhav-VirtualBox:~$ cd /home/vaibhav/Java
vaibhav@vaibhav-VirtualBox:~/Java$ ls -al
total 20
drwxr-xr-x  2 vaibhav vaibhav 4096 Jan 18 16:52 .
drwxr-xr-x 25 vaibhav vaibhav 4096 Jan 18 16:50 ..
-rw-r--r--  1 vaibhav vaibhav  990 Jan 18 16:52 FileList.class
-rw-r--r--  1 vaibhav vaibhav  477 Jan 18 16:52 FileList.java
-rw-r--r--  1 vaibhav vaibhav  487 Jan 18 16:52 FileList.java~

When I changed String dirname to /home/vaibhav/Java which is pwd too, program executed well.

What was the issue? Thank you.

Mmmh ... I doubt this, why we don't get output from print. I think sl is null. What gives f1.isDirectory(). — PeterMmm
– PeterMmm, Commented Jan 18, 2014 at 12:03
no, sl isn't null. I added 2 files to it, before running code. — javaEntu
– javaEntu, Commented Jan 18, 2014 at 12:07

Raj · Accepted Answer · 2014-01-18 12:08:19Z

0

Better to try this:

File folder = new File("your/path");
File[] listOfFiles = folder.listFiles();

    for (int i = 0; i < listOfFiles.length; i++) {
      if (listOfFiles[i].isFile()) {
        System.out.println("File " + listOfFiles[i].getName());
      } else if (listOfFiles[i].isDirectory()) {
        System.out.println("Directory " + listOfFiles[i].getName());
      }
    }

Hope this helps you

answered Jan 18, 2014 at 12:08

Raj

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7 Comments

javaEntu Over a year ago

I tried that too before posting here. But one post stackoverflow.com/a/11643057/2642938 said that using list() is better than using listFiles(). My main question is "When I changed String dirname to /home/vaibhav/Java which is pwd too, program executed well."

Raj Over a year ago

can you explain more clearly what is your requirement exactly @VAL

javaEntu Over a year ago

To display file lists from .../Test dir. @SanthoshKumar544

Raj Over a year ago

so what ever the answer i posted definitely displays file lists from your desired path and also including directories @VAL

javaEntu Over a year ago

yeah, I don't know why it didn't display it before that! That's why I posted it here. Now after changing dirname multiple times its working well.

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