StateTracker.java revision 2362
2362N/A * Copyright (c) 2007, Oracle and/or its affiliates. All rights reserved. 0N/A * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 0N/A * This code is free software; you can redistribute it and/or modify it 0N/A * under the terms of the GNU General Public License version 2 only, as 2362N/A * published by the Free Software Foundation. Oracle designates this 0N/A * particular file as subject to the "Classpath" exception as provided 2362N/A * by Oracle in the LICENSE file that accompanied this code. 0N/A * This code is distributed in the hope that it will be useful, but WITHOUT 0N/A * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 0N/A * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 0N/A * version 2 for more details (a copy is included in the LICENSE file that 0N/A * accompanied this code). 0N/A * You should have received a copy of the GNU General Public License version 0N/A * 2 along with this work; if not, write to the Free Software Foundation, 0N/A * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 2362N/A * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 2362N/A * or visit www.oracle.com if you need additional information or have any 0N/A * This interface is used to track changes to the complex data of an 0N/A * object that implements the StateTrackable interface. 0N/A * The usage pattern for code accessing the trackable data is as follows: 0N/A * StateTrackable trackedobject; 0N/A * MyInfo cacheddata; 0N/A * StateTracker cachetracker; 0N/A * public synchronized MyInfo getInfoAbout(StateTrackable obj) { 0N/A * if (trackedobject != obj || !cachetracker.isCurrent()) { 0N/A * // Note: Always call getStateTracker() before 0N/A * // caching any data about the objct... 0N/A * cachetracker = obj.getStateTracker(); 0N/A * cacheddata = calculateInfoFrom(obj); 0N/A * trackedobject = obj; 0N/A * return cacheddata; 0N/A * Note that the sample code above works correctly regardless of the 0N/A * {@link StateTrackable.State State} of the complex data of the object, 0N/A * but it may be inefficient to store precalculated information about 0N/A * an object whose current {@link StateTrackable.State State} is 0N/A * {@link StateTrackable.State#UNTRACKABLE UNTRACKABLE} 0N/A * and it is unnecessary to perform the {@link #isCurrent} test for 0N/A * data whose current {@link StateTrackable.State State} is 0N/A * {@link StateTrackable.State#IMMUTABLE IMMUTABLE}. 0N/A * Optimizations to the sample code for either or both of those terminal 0N/A * States may be of benefit for some use cases, but is left out of the 0N/A * example to reduce its complexity. 0N/A * @see StateTrackable.State 0N/A * An implementation of the StateTracker interface which 0N/A * always returns true. 0N/A * This implementation is useful for objects whose current 0N/A * {@link StateTrackable.State State} is 0N/A * {@link StateTrackable.State#IMMUTABLE IMMUTABLE}. 0N/A * An implementation of the StateTracker interface which 0N/A * always returns false. 0N/A * This implementation is useful for objects whose current 0N/A * {@link StateTrackable.State State} is 0N/A * {@link StateTrackable.State#UNTRACKABLE UNTRACKABLE}. 0N/A * This implementation may also be useful for some objects 0N/A * whose current {@link StateTrackable.State State} is 0N/A * {@link StateTrackable.State#DYNAMIC DYNAMIC}. 0N/A * Returns true iff the contents of the complex data of the 0N/A * associated StateTrackable object have not changed since 0N/A * the time that this StateTracker was returned from its 0N/A * getStateTracker() method. 0N/A * @see StateTrackable