Stopping a thread from running

Question

Hai
     I am new to java. It would be helpful for me if someone helps me out in doing this.
     Actually in my program ,I should
i. Find out whether a particular file exists in the given directory or not.
ii. If the file doesn't exist, my program should wait for certain timeframe and check for the same file again.
iii. If the program cannot find the required file within the timeout specified, my application should exit.
     I have done (i) and (ii) using threads. But in the case of (iii), I came to know that stop() method is depricated.
     I am providing my code for a better understanding. Could you please let me know, what would be the best way to stop the thread from running after the timeout is reached in my program?
Thanx in advance
import java.io.File;
public class Fileexists implements Runnable
static Thread t;
public static void main(String[] args)
     System.out.println("creation of object");     
     FileExists test = new FileExists();
     t = new Thread(test);
     t.start();
// run method
public void run()
     File f = new File("searchfile.txt");
     boolean b = f.exists();
System.out.println();
if(b == false)
System.out.println("Required file doesnot exists");
try
     t.sleep(20000);
catch (InterruptedException e)
     // TODO Auto-generated catch block
     e.printStackTrace();
          t.run();
else
System.out.println("Required file found");
} // end of run()
} // end of FileExists class

Answer 1

Actually your use of threads is a difference which makes no difference. The JVM starts an initial thread and runs your main(), at the end of which you start a thread and return. So you've just replaced one thread with another. There's no parallel processing.
The t.run() at the end of your run() method won't work. A particular Thread object can only run once. It will give you an IllegalStateException.
I can't see how multi-threading will help you with this task at all, all you need is a simple loop with a Thread.sleep in it.
If you really want to use a separate thread or Timer to implement a timeout (as an exercise) then use Thread.interrupt() to wind up a thread. The looping thread should test with Thread.interrupted() in it's loop condition, if it's in sleep() when interrupted an InterruptedException will be thrown which you should catch and allow to break the loop and let the thread terminate.
So your loop structure looks like:
try {
while(!Thread.interrupted()) {
    ...  do your test
    Thread.sleep(.....);
  System.out.println("Thread terminated by detecting interrupted");
  } catch(InterruptedException ex)  {
     System.out.println("Thread interrupted from sleep");
You can get the Thread for the main thread simply by storing Thread.currentThread() in a Thread reference.
I'd suggest using a java.util.Timer to launch your time-out and leave the loop on the main thread started by the JVM.