001// License: GPL. For details, see LICENSE file.
002package org.openstreetmap.josm.gui.util;
003
004import javax.swing.event.ChangeEvent;
005import javax.swing.event.ChangeListener;
006import javax.swing.event.EventListenerList;
007
008/**
009 * Replacement to {@code java.util.Observable} class, deprecated with Java 9.
010 * @since 10210
011 */
012public class ChangeNotifier {
013
014    /** Stores the listeners on this model. */
015    private final EventListenerList listenerList = new EventListenerList();
016
017    /**
018     * Only one {@code ChangeEvent} is needed per button model
019     * instance since the event's only state is the source property.
020     * The source of events generated is always "this".
021     */
022    private ChangeEvent changeEvent;
023
024    /**
025     * Adds a {@code ChangeListener}.
026     * @param l the listener to add
027     */
028    public final void addChangeListener(ChangeListener l) {
029        listenerList.add(ChangeListener.class, l);
030    }
031
032    /**
033     * Removes a {@code ChangeListener}.
034     * @param l the listener to add
035     */
036    public final void removeChangeListener(ChangeListener l) {
037        listenerList.remove(ChangeListener.class, l);
038    }
039
040    /**
041     * Notifies all listeners that have registered interest for notification on this event type.
042     * The event instance is created lazily.
043     */
044    protected final void fireStateChanged() {
045        // Guaranteed to return a non-null array
046        Object[] listeners = listenerList.getListenerList();
047        // Process the listeners last to first, notifying those that are interested in this event
048        for (int i = listeners.length-2; i >= 0; i -= 2) {
049            if (listeners[i] == ChangeListener.class) {
050                // Lazily create the event:
051                if (changeEvent == null)
052                    changeEvent = new ChangeEvent(this);
053                ((ChangeListener) listeners[i+1]).stateChanged(changeEvent);
054            }
055        }
056    }
057}