Lack of randomness in my threads

Question

Hi, I have the following code:
import java.util.Collections;
import java.util.List;
import java.util.LinkedList;
import java.util.Iterator;
public class ThreadSafeCollection {
     public static void main(String args[]) throws Exception {
          List queue = Collections.synchronizedList(new LinkedList());
          LinkedList threads = new LinkedList();
          int i = 0;
          while(i < 25) {
               threads.add(new InsertMessages("Thread" + i, queue));
               i++;
          Iterator iterator = threads.iterator();
          while(iterator.hasNext()) {
               ((InsertMessages)iterator.next()).start();
          Thread.sleep(2000);
          System.out.println("threads contains " + threads.size());
          System.out.println("queue contains " + queue.size() + " items.");
class InsertMessages extends Thread {
     List queue;
     final static int maxIterations = 10;
     public InsertMessages(String threadName, List queue) {
          super(threadName);
          this.queue = queue;
     public void run() {
          int iterations = 0;
          try {
               Thread.sleep((int)Math.random() * 1000);
          catch(InterruptedException e) {
               System.err.println("something");               
          while(iterations < maxIterations) {
               queue.add(getName() + " at iteration " + iterations);
               iterations++;                    
This above code produce the following results for the queue:
Thread0 at iteration 0, Thread0 at iteration 1, Thread0 at iteration 2, Thread0 at iteration 3, Thread0 at iteration 4, Thread0 at iteration 5, Thread0 at iteration 6, Thread0 at iteration 7, Thread0 at iteration 8, Thread0 at iteration 9, Thread1 at iteration 0, Thread1 at iteration 1, Thread1 at iteration 2, Thread1 at iteration 3, Thread1 at iteration 4, Thread1 at iteration 5.....
My problem is that the Thread execute in order from 1 to 10. This seems very deterministic. I expected more randomness. i.e. I expected the order of thread execution to be something like this: Thread3, Threads8, Thread1, Thread7... Any ideas why this is happening?
Thanks,
Paul0al

Answer 1

This is happening because you are inserting the threads into this list, then you are starting them in the same order. So one starts, runs, sleeps, the second starts, runs, sleeps, etc... So of course they go in order. However, if you left it running a long time, it's not impossible that due to factors beyond your control, one thread might sleep a little longer or shorter and therefore cause the threads to start running in different orders, but even that will likely remain in the same different order for some period of time.
If you really are wanting to start them in any order, then put the threads in a collection that doesn't guaranty an order (like Hashtable) and then get an iterator and start them. The other thing to do would be to start threads and have the sleep time be some random value each time to.