Why does fireTableChanged() on AbstractTableModel notify listeners last to first?

Question

This is obscure, but for some reason the notification in AbstractTableModel is last-to-first, causing a bug in my code. I can fix it, but I'm wondering if anyone knows why notification is done in this way?

public void fireTableChanged(TableModelEvent e) {
    // Guaranteed to return a non-null array
    Object[] listeners = listenerList.getListenerList();
    // Process the listeners last to first, notifying
    // those that are interested in this event
    for (int i = listeners.length-2; i>=0; i-=2) {
        if (listeners[i]==TableModelListener.class) {
        ((TableModelListener)listeners[i+1]).tableChanged(e);
        }
    }
}

Why do you need your listeners to fire in a certain order? That's a design smell. — Platinum Azure, Mar 01 '12 at 20:06
*"last-to-first, causing a bug in my code."* No, the bug in your code was caused by presuming the order in the first place. Fix that and the rest becomes irrelevant. — Andrew Thompson, Mar 01 '12 at 20:19

score 3 · Accepted Answer · answered Mar 01 '12 at 20:28

3

I don't think there is a real reason for it.

Maybe they wanted extra-safety in case a listener is removes itself from the list of listeners while the event is fired (i.e. while we are still iterating over the listeners-list).

Although this would not really be necessary as the listenerList is copy-on-write...

answered Mar 01 '12 at 20:28

alex

1,229
7
6

+1 See also this [Q&A](http://stackoverflow.com/questions/2159803/eventlistenerlist-firing-order). The [relevant API](http://docs.oracle.com/javase/7/docs/api/javax/swing/event/EventListenerList.html) expands on the rationale. – trashgod Mar 01 '12 at 22:49

score 1 · Answer 2 · answered Mar 01 '12 at 20:10

1

Listeners get put into a Stack. So when they are notified they are "pop"ed out of the stack in the reverse order in which they are put in.

If the order of the listeners matter, you should try to resolve that without caring which order they are checked in. If it does matter, change the order you add the listeners.

answered Mar 01 '12 at 20:10

Avogadro

353
2
11

Conceptually, perhaps. They are actually stored in an [`EventListenerList`](http://docs.oracle.com/javase/7/docs/api/javax/swing/event/EventListenerList.html). – trashgod Mar 01 '12 at 22:47

Why does fireTableChanged() on AbstractTableModel notify listeners last to first?

2 Answers2