NotificationEmitterSupport.java 文件源码

public void addNotificationListener(NotificationListener listener,
                                    NotificationFilter filter,
                                    Object handback) {

    if (listener == null) {
        throw new IllegalArgumentException ("Listener can't be null") ;
    }

    /* Adding a new listener takes O(n) time where n is the number
       of existing listeners.  If you have a very large number of
       listeners performance could degrade.  That's a fairly
       surprising configuration, and it is hard to avoid this
       behaviour while still retaining the property that the
       listenerList is not synchronized while notifications are
       being sent through it.  If this becomes a problem, a
       possible solution would be a multiple-readers single-writer
       setup, so any number of sendNotification() calls could run
       concurrently but they would exclude an
       add/removeNotificationListener.  A simpler but less
       efficient solution would be to clone the listener list
       every time a notification is sent.  */
    synchronized (listenerLock) {
        List<ListenerInfo> newList = new ArrayList<>(listenerList.size() + 1);
        newList.addAll(listenerList);
        newList.add(new ListenerInfo(listener, filter, handback));
        listenerList = newList;
    }
}