You probably screwed up on the initialisation. You must create a
mother ArrayList and 3 child ArrayLists and put them in the mother
before you can even think about filing your objects.

This should do all you ask for:

import java.util.ArrayList;
import java.util.Iterator;

public class array
{
   static public void main(String[] args)
   {
    ArrayList parent = new ArrayList();
    {
       ArrayList child = new ArrayList();
       child.add( "A" );
       child.add( "B" );
       child.add( "C" );
       parent.add( child );
    }

    {
       ArrayList child = new ArrayList();
       child.add( "D" );
       child.add( "E" );
       parent.add( child );
    }

    {
       ArrayList child = new ArrayList();
       child.add( "F" );
       child.add( "G" );
       child.add( "H" );
       child.add( "I" );
       parent.add( child );
    }

    /*
    * Following prints "parent has 3 elements" which is what we
    * expect
    */
    System.out.println("parent has " +parent.size()+ " elements." );

    /*
    * The following loop prints:
    *     A B C
    *     D E
    *     F G H I
    */
    for (Iterator parentIterator = parent.iterator() ;
        parentIterator.hasNext() ;
        ) {
       ArrayList child = (ArrayList)parentIterator.next();
       for (Iterator childIterator = child.iterator() ;
        childIterator.hasNext() ;
        ) {
        String str = (String)childIterator.next();
        System.out.print(str + " " );
       }
       System.out.println();
    }
    System.out.println();

    /*
    * Accessing individual elements of the array -- Need the ugly
    * typecasts (with Java 1.4)
    */
    System.out.println("Element ( 1, 1 ) is: " +
              ((ArrayList)parent.get(1)).get(1));
    System.out.println("Element ( 0, 2 ) is: " +
              ((ArrayList)parent.get(0)).get(2));
    System.out.println("Element ( 2, 2 ) is: " +
              ((ArrayList)parent.get(2)).get(2));
    System.out.println();

    /*
    * Access an element outside the range, and you get an
    * java.lang.IndexOutOfBoundsException
    */
    System.out.println("Element ( 1, 3 ) is: " +
              ((ArrayList)parent.get(1)).get(3));
   }
}