I/O Error in File.listFiles()

Question

Basically, I have the following piece of code:
public static void main(String[] args) {
    File f = new File("C:\\");
    search(f);
public static void search (File f) {
    if(f.isFile()) {
        if(contain(getEnd(f)))
            files.add(f);
    } else
        for(int i = 0; i < f.listFiles().length; i++) {
            search(f.listFiles());
}And a NullPointerException is thrown from this line: for(int i = 0; i < f.listFiles().length; i++) {
The source of the exception is obviously (correct me if I'm wrong) the listFiles() method, but "C:\\" does denote a directory, therefore this should have something to do with the I/O Error which may occur, according to the java API.
The API doesn't say much more about the I/O error, so my question is what could have caused it to occur, and what can be done to correct this issue?
Thanks in advance. =]
Edited by: Hirsch on Sep 11, 2008 2:23 PM                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       

Answer 1

The API clearly states that listFiles() can return null. I would prefer it returned an empty array, but no one asked me first.
Conclusion: look before you leap!
public static void search (File f) {
    if(f.isFile()) {
    } else {
        File[] files = f.listFiles();
        if (files != null) {
            for(File file : files) {
                search(file);
}another variation:
import java.io.*;
public class Example {
    public static void main(String[] args) {
       search(new File(".."));
    public static void search (File... files) {
        if (files != null) {
            for(File f : files) {
                if (f.isFile()) {
                } else if (f.isDirectory()) {
                    search(f.listFiles());
                } else {
}