Retrieving a file

Question

Hi!
I would like to find a file (doc.xml) in my architecture, at the second level bottom.
For this, I use the following code:
import java.io.*;
import java.util.*;
public class recherche extends Object {
public static void main (String args[]) throws Exception
/*org.apache.xalan.xslt.Process.main(new String[] {"-IN", "C:/WINDOWS/Bureau/DGA/AIS/cyril/DERA/HP/61DG019H0035/doc.xml",
"-XSL", "C:/WINDOWS/Bureau/DGA/AIS/cyril/DERA/HP/61DG019H0035/doc.xsl"});*/
File f = new File("C:/WINDOWS/Bureau/DGA/AIS/cyril/DERA");
File [] files = f.listFiles();
for (int i=0; i<files.length; i++)
System.out.println(files.getName());
File [] sfiles = files[i].listFiles();
for (int j=0; j<sfiles.length; j++)
System.out.println(sfiles[j].getName());
File [] ssfiles = sfiles[j].listFiles();
for (int k=0; k<ssfiles.length; k++)
System.out.println(ssfiles[k].getName());
/*if (ssfiles[k].getName() == "doc.xml")
System.out.println(ssfiles[k].getName());
For the levels i and j, the program runs well, but not for the third level k.
I have the following error message:
Exception in thread "main" java.lang.NullPointerException at recherche.main (recherche.java:21).
Some of you know how to fix this,
REgards,
Steev

Answer 1

Copying your code into an editor, line 21 (where the exception is thrown) is the final loop. In this case it looks like you are calling File[].length on a null array, which will of course throw a null pointer exception. The array is null because only a directory has sub-files.
You list the files of each file in the file system. You should be only listing the files of directories.
example:
File f=new File("C:\\"); //just an example base-file
if (f.isDirectory()) {
  File[] files=f.listFiles();
  for (int i=0; i<files.length; i++) {
    //etc
}Alternatively, you can check for null:
File f=new File("C:\\");
File[] files=f.listFiles();
if (files != null) {
  for (int i=0; i<files.length; i++) {
    //etc
}Hope this helps.