java - What are the possible problems caused by adding elements to unsynchronized ArrayList's object by multiple threads simultaneously?

What are the possible problems caused by adding elements
to unsynchronized ArrayList's object by multiple threads
simultaneously?

Tried to run some experiments
with a static ArrayList with multiple threads but couldn't find
much.

Here i am expecting much of the side
effects of not synchronizing an ArrayList or like Objects in a multithreaded
environment.

Any good example showing side
effects would be
appreciable.
thanks.

below
is my little experiment which ran smoothly without any
exception.

I also wonder why it
didn't throw any
ConcurrentModificationException?

import
            java.util.ArrayList;
import java.util.List;

public class
            Experiment {
 static List list = new
            ArrayList();

 public static void main(String[] args)
            {
 for (int i = 0; i < 10; i++) {
 System.out.println("A " +
            i);
 new Thread(new Worker(list, "" + i)).start();
 }
 }
            
}

class Worker implements Runnable {

            List al;

 String name;

 public
            Worker(List list, String name) {
 this.al = list;

            this.name = name;
 }

 @Override
 public void
            run() {
 while (true) {

 int no = (int) (Math.random() *
            10);
 System.out.println("[thread " + name + "]Adding:" + no + "to Object id:"
            + System.identityHashCode(al));
 al.add(no);
 }

            }
}