Calling a method in a class extended from thread

Question

I'm trying to use two threads of type ThreadTest to call the addNum method in the class below. I found that i couldnt call the addnum method with the instances I created but had to make the addnum method static and then call it with the class name ThreadTest.Is there anyway to get round this? i'm doing this exercise to try and understand synchronisation. Thanks
import java.lang.Thread;
import java.util.*;
class ThreadTest extends Thread implements Runnable{
     private int x;
     private static ArrayList intnumbers = new ArrayList();
     public ThreadTest(int no)
          x=no;
     public void run()
          for (int i=0; i<x; i++)
               try
               System.out.println(i);
               Thread.currentThread().sleep((long)(Math.random() * 1000));
          }catch(InterruptedException e ){e.getMessage();}
     public static void addNum(int n)
          synchronized(intnumbers){
                    intnumbers.add(new Integer(n));
public static void main(String[] args)
     Thread  testThread = new Thread(new ThreadTest(50));
     Thread  testThreadb = new Thread(new ThreadTest(50));
     testThread.start();
     testThreadb.start();
          ThreadTest.addNum(10);
    //*** this gives an error
    //testThread.addNumber(10);
    //testThreadb.addNumber(10);
}

Answer 1

ok here goes again. ;).
import java.lang.Thread;
import java.util.*;
class ThreadTest extends Thread implements Runnable{
     private int x;
     private static ArrayList intnumbers = new ArrayList();
     public ThreadTest(int no)
          x=no;
     public void run()
          for (int i=0; i<x; i++)
               try
               System.out.println(i);
               Thread.currentThread().sleep((long)(Math.random() * 1000));
          }catch(InterruptedException e ){e.getMessage();}
     public static void addNum(int n)
          synchronized(intnumbers){
                    intnumbers.add(new Integer(n));
public static void main(String[] args)
     Thread  testThread = new ThreadTest(50);
     testThread.start();
     //gives error so how can i create 2 instances of testThread and call addNum with them?
     //testThread.addNum(10);
//works ok but I want to call addNum with 2 different threads
     ThreadTest.addNum(10);
}