code: public void setValue(int index, String value) {
          index += getIndexOffset();
          listBox.setValue(index, value);
          reload();
      }
docs: Sets the value associated with the item at a given index. This value can
  be used for any purpose, but is also what is passed to the server when
  the list box is submitted as part of a {@link FormPanel}.
  
  @param index the index of the item to be set
  @param value the item's new value; cannot be <code>null</code>
  @throws IndexOutOfBoundsException if the index is out of range