need an index of latest item choosen with ListBox

The ordinal index of the selected option, starting from 0. The value -1 is returned if no element is selected. If multiple options are selected, the index of the first selected option is returned.

I face issue while prihibiting the multiselect option with the help of control key.
List box should not be even the multiselect box,

int index = ((XXXListBox) event.getSource()).getSelectedIndex();

Here the index returned is index of the first selected option is returned. what can be done inorder to get index of last choosen item in the list of items, if multiple items are choosen with the help of contorl key or dragging continuously.