001    /*
002     * JBoss DNA (http://www.jboss.org/dna)
003     * See the COPYRIGHT.txt file distributed with this work for information
004     * regarding copyright ownership.  Some portions may be licensed
005     * to Red Hat, Inc. under one or more contributor license agreements.
006     * See the AUTHORS.txt file in the distribution for a full listing of 
007     * individual contributors.
008     *
009     * JBoss DNA is free software. Unless otherwise indicated, all code in JBoss DNA
010     * is licensed to you under the terms of the GNU Lesser General Public License as
011     * published by the Free Software Foundation; either version 2.1 of
012     * the License, or (at your option) any later version.
013     * 
014     * JBoss DNA is distributed in the hope that it will be useful,
015     * but WITHOUT ANY WARRANTY; without even the implied warranty of
016     * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
017     * Lesser General Public License for more details.
018     *
019     * You should have received a copy of the GNU Lesser General Public
020     * License along with this software; if not, write to the Free
021     * Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
022     * 02110-1301 USA, or see the FSF site: http://www.fsf.org.
023     */
024    package org.jboss.dna.graph.observe;
025    
026    import net.jcip.annotations.ThreadSafe;
027    
028    /**
029     * Interface used to register {@link ChangeObserver listeners}. Implementations should use a {@link ChangeObservers} to actually
030     * manage the listeners.
031     */
032    @ThreadSafe
033    public interface Observable {
034    
035        /**
036         * Register the supplied observer. This method does nothing if the observer reference is null.
037         * 
038         * @param observer the observer to be added; may be null
039         * @return true if the observer was added, or false if the observer was null, if the observer was already registered, or if
040         *         the observer could not be added
041         */
042        boolean register( ChangeObserver observer );
043    
044        /**
045         * Unregister the supplied observer. This method does nothing if the observer reference is null.
046         * 
047         * @param observer the observer to be removed; may not be null
048         * @return true if the observer was removed, or false if the observer was null or if the observer was not registered on this
049         *         source
050         */
051        boolean unregister( ChangeObserver observer );
052    
053    }