Using thread to read a big number of files

Question

Hi all,
I got a question with THREAD. Can you help me, please?
I have a class, PragFileLoader, to read many files in a folder. First readDir() reads whole directory and gets a list of file name. Then readFile() reads each file. And finally readLine() reads each line in a file. The problem here is a big number of files. So I have to construct many instances of PragFileLoader. However I should use some kind of lock in a file, which is read by certain PragFileLoader, to let other instances of PragFileLoader know that it's locked therefore these instances won't read the locked file, they gonna to read other files.
import java.io.*;
import java.util.Vector;
public class PragFileLoader extends Thread{
    private Vector v;
     * Constructor
    public PragFileLoader() {
        v = new Vector();
     * Read a line
     * @param str a line to read
    public TrafficDataObject readLine(String fN, String str) {
        // Do something
    public synchronized void readFile(String fileName, File in, File err, File done) {
        try {
            Thread.sleep((int) (Math.random() * 100));
              // Do something           
        } catch (IOException e) {
            e.printStackTrace();  //To change body of catch statement use File | Settings | File Templates.
        } catch (InterruptedException e) {
            e.printStackTrace();  //To change body of catch statement use File | Settings | File Templates.
        notifyAll();
    public void readDir() {
        //   Vector v = new Vector();
        File in = new File(Preferences.PRAGINBOX);
        File err = new File(Preferences.PRAGERROR);
        err.mkdirs();
        File done = new File(Preferences.PRAGDONE);
        done.mkdirs();
        String[] fileName = in.list();
        for (int i = 0; i < fileName.length; i++) {
            //readFile(fileName, v, in, err, done);
readFile(fileName[i], in, err, done);
public Vector getV(){
return v;
public void run() {
for (int i = 0; i < 10; i++) {
readDir();
try {
Thread.sleep((int) (Math.random() * 100));
} catch (InterruptedException e) {
And in main() I construct 10 instances of PragFileLoader and I got nothing

Answer 1

Do you have to make readDir() part of PragFileLoader?
Why don't you first read the directory once, and then assign the files to a thread each. I don't think it's efficient to have too many file reading threads running at the same time.