I have an application that is grabbing images from a video camera and dumping them in a directory. I needed a way to count how many images were in the folder as the program went along. If you ever needed such a function, here is code that does it (just change the path and the file suffix to whatever is useful to you):

void setup() {

 size (250, 250);

    File imageDir = new File("/Users/mccoy/Pictures/processing/set1/");

    FilenameFilter ff = new FilenameFilter() {
      public boolean accept(File imageDir, String name) {
         return name.endsWith(".bmp");
          }
        };

     String[] theList = imageDir.list(ff);
     int bmpCount = theList.length;
     println(str(bmpCount) + " image files");
}

Thanks for sharing this code...it's exactly what I was looking for!
A