Multithreading in Java - don't know what's causing this exception

[P00dle]

I've written the code already, and it compiles, but gets the following runtime exception:
java.lang.IllegalThreadStateException
at java.lang.Thread.start(Thread.java:595)
at threads.ThreadStarter.run(ThreadStarter.java:52)
at java.lang.Thread.run(Thread.java:619)

I've higlighted the line that throws the exception. I have no idea what's wrong, my knowledge in threads is sadly lacking.

If anyone could help me out it would be great.

package threads;

// Create a thread
import java.io.File;

class ThreadStarter implements Runnable {
    public static void main(String[] args) {
        // This thread will scan the folders every 2 minutes, and assign other ThreadStarter to handle files found in the directories
        while (true) {
            new ThreadStarter().Threads();
            try {
                Thread.sleep(60000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
    // This should scan the directory every 2 minutes

    Thread masterThread;

    void Threads() {
        // Create a second thread - this thread will handle the files found in the folder
        masterThread = new Thread(this, "first child");
        masterThread.start();
    }

    // Entry point for second thread
    public void run() {
        // TODO:: Make more ThreadStarter
        Thread currentThread = Thread.currentThread();
        Thread firstThread = new Thread();
        Thread secondThread = new Thread();
        String fileName = "";

        while (masterThread == currentThread) {
            // Scan the folders, assign the files to ThreadStarter for processing
            File main_dir = new File("C:\\Thread test");

            File[] child_dirs = main_dir.listFiles();

            for (int i = 0; i < child_dirs.length; i++) {
                // [get filename] dir_name = child_files[i].getName();
                // start thread to look for files in this dir.
                File[] new_files = child_dirs[i].listFiles();
                // create ThreadStarter for each of the contained files, up to a limit of 3 ThreadStarter.
                try {
                    for (int ii = 0; ii < new_files.length; ii++) {
                        fileName = new_files[ii].getName();
                        if (!firstThread.isAlive()) {
                            // Assign firstThread the task of handling the file
                            [B]firstThread.start();[/B]
                        } else if (!secondThread.isAlive()) {
                            // Assign secondThread the task of handling the file
                            secondThread.start();
                        }
                    }
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }

            while (firstThread == currentThread) {
                try {
                    // Handle file
                    File file = new File(fileName);
                    // Destination directory
                    File dir = new File("C:\\Thread test\\retain");
                    // Move file to new directory
                    boolean success = file.renameTo(new File(dir, file.getName()));
                    System.out.println(fileName + " was moved succesfully");
                    if (!success) {
                        System.out.println(fileName + " was not moved succesfully");
                    }
                    Thread.sleep(5000);

                    firstThread.join();
                } catch (InterruptedException ie) {
                    ie.printStackTrace();
                }
            }

            while (secondThread == currentThread) {
                try {
                    //Handle file
                    File file = new File(fileName);
                    // Destination directory
                    File dir = new File("C:\\Thread test\\retain");
                    // Move file to new directory
                    boolean success = file.renameTo(new File(dir, file.getName()));
                    System.out.println(fileName + " was moved succesfully");
                    if (!success) {
                        System.out.println(fileName + " was not moved succesfully");
                    }
                    Thread.sleep(5000);

                    secondThread.join();
                } catch (InterruptedException ie) {
                    ie.printStackTrace();
                }
            } 
        }
    }
}

[jwenting]

You have no Runnable instance attached to the Threads.

[moutanna]

Hi;
the

!(t.isAlive())  //NOT isAlive

return true if the traed upon wict it is called hase been moved to the dead state; and as the dead thread can never enter any other state not even if the start method is invoked in it;
That is why you receive the exception; a dead thread could never become alive.
You should us a fresh, create a new one;
As follow:

t=new Test (); //Create it here
t.start();

Hope it helps.