ArrayList, Collections.synchronizedList and CopyOnWriteArrayList with null simulator

NullSimulator

package com.srini.util;

import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.concurrent.CopyOnWriteArrayList;

public class NullSimulator implements Runnable
{
	public static Map<String,List<String>> map=new HashMap<String, List<String>>();
	
	public static void main(String[] args) throws InterruptedException 
	{
		List<String> list= new CopyOnWriteArrayList<String>();//Collections.synchronizedList(new ArrayList<String>());new ArrayList<String>();

		for(int i=0;i<50000;i++)
		{
			list.add(String.valueOf(i));
		}
		map.put("val", list);
		for (int i=0;i<2;i++){
			new Thread(new NullSimulator(),String.valueOf(i)).start();
		}
	}
	
	@Override
	public void run() 
	{
	   List<String> lst=map.get("val");
	   if(lst!=null&lst.size()>0){
		   for(int i=0;i<lst.size();i++){
			   lst.add(lst.get(i));
			   lst.remove(i);
			   map.put("val", lst);
			   if(map.get("val").contains(null))
			   {
				   System.out.println((i+1)+"- "+(Integer.parseInt(Thread.currentThread().getName())+1));
				   return;
				  // throw new NullPointerException();
			   }
			   //else System.out.println("no null");
			   
		   }
	   }
	}

}