Question

I have a JList that lists an arrayList. When I press the button called delete I want to delete the selected element from the list (and ideally the arraylist). At the moment I have the following code, however it is not working. By this I mean that it seems to do nothing if an element is selected and it gives me a ArrayIndexOutOfBoundsException when nothing is selected.

private JList listOrders = new JList(arrayList.toArray());

public void myList() {
    listOrders.setSelectionMode(ListSelectionModel.SINGLE_INTERVAL_SELECTION );
    panelForLists.add(listOrders);
}

public void updateList() {
    listOrders.setListData(arrayList.toArray());
    listOrders.revalidate();
    listOrders.repaint();
}

public void actionPerformed(ActionEvent event) {
    if (event.getSource() == deleteItem) {
         int index = listOrders.getSelectedIndex();
            listOrders.remove(index);
           updateList();
    }
}

I assume that maybe it’s because I have to add in a ListSelectionListener somewhere, but I don’t know how I can work this. I’ve searched on the internet for an answer for ages and this was what I came up with from the JList oracle demo.

Thanks a lot!

Answer 1

This is basically what Hovercraft Full Of Eels already answered, but with some more code pointers.

1. You indeed remove and re-add the element, which of course has no effect. The easiest would be if your ArrayList could be used directly as ListModel but this is not possible (as the ArrayList does not fire any events). You might be tempted to use the JList( Vector ) constructor instead, but that one does not allow to modify the vector afterwards. So you are stuck with creating your own ListModel. The DefaultListModel class is probably just what you are looking for.
2. The code in your actionPerformed method always assume there is an element selected. Note that the getSelectedIndex method returns -1 when nothing is selected. The best thing you could do (for the user) is to disable the delete button when nothing is selected, or when more then one element is selected. This can be achieved by letting the action behind the button listen to the selection model of the list, and update its enabled state depending on the selection (do not forget to fire a PropertyChangeEvent if needed). If you do not work with an Action backing up the button, just switch the enabled state of the button directly based on the selection.