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 }