How to access folder contents dynamically

i have used the following method, am using netbeans IDE.
<pre>
public static List getImages(){
List l1=new ArrayList();
File dir = new File("../build/web/politicalimages");

// array of supported extensions (use a List if you prefer)
final String[] EXTENSIONS = new String[]{
"gif", "png", "jpg" // and other formats you need
};
// filter to identify images based on their extensions
FilenameFilter IMAGE_FILTER = new FilenameFilter() {
public boolean accept(final File dir, final String name) {
for (final String ext : EXTENSIONS) {
if (name.endsWith("." + ext)) {
return (true);
}
}
return (false);
}
};
if (dir.isDirectory()) { // make sure it's a directory
for (final File f : dir.listFiles(IMAGE_FILTER)) {
BufferedImage img = null;

try {
img = ImageIO.read(f);

// you probably want something more involved here
// to display in your UI
String imagepath= f.getName();
System.out.println("image path in dao class......."+imagepath);
l1.add(f);

}
catch (final IOException e) {
// handle errors here

}
}
}
return l1;
}
</pre>
but it returns null when i get the list values. how can i give netbeans folder path.