Monitor changes to a collection

Question

Say you have the following java bean:

public class MyBean
{
    private List<String> names = new ArrayList<String>();

    public void addName(String name)
    {
        names.add(name);
        fireNamesPropertyChange(name);
    }
}

How would you normally implement a property change event for a collection? Do you try and use the index property which seems to be more for arrays than collections?

Answer 1

(NOTE: I updated this post after realizing a few mistakes of my own so this isn't the original but a more refined one instead)

For this purpose I'd do two new interfaces, ListListener and Listenable and then I would create a new class like ListenableArrayList which would wrap every List method with a call to one (or more) relevant methods defined in ListListener. In code it'd be something like this:

public class ListenableArrayList<T> extends ArrayList<T>
                                    implements Listenable<T> {

    private ArrayList<T> internalList;
    private ListListener<T> listener;

    /* .. */

    public void add(T item) {
        listener.beforeAdd(T item);
        internalList.add(item);
        listener.afterAdd(T item);
    }

    /* .. */

    public void setListener(ListListener<T> listener) {
        this.listener = listener;
    }

}

public interface ListListener<T> {
    /* .. */
    void beforeAdd(T item);
    void afterAdd(T item);
    /* .. */
}

public interface Listenable<T> {
    /* .. */
    void setListener(ListListener<T> listener);
    /* .. */
}

The reason I'd do it this way would be to allow for creating truly ad-hoc listeners on the fly instead of tying the ListenableArrayList to some specific implementation. For example with this the following would be possible:

Listenable<String> list = new ListenableArrayList<String>();

list.setListener(new ListListener<String>() {
    @Override
    public void beforeAdd(String item) {
        System.out.println("About to add element "+item+"...");
    }
    @Override
    public void afterAdd(String item) {
        System.out.println("...element "+item+" has been added.");
    }
});

A bit cluttered, maybe but on the other hand this would allow for easy extension to Collections, Sets and whatnot rather easily.