/* * Copyright (c) 2007, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation.  Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ package sun.java2d; /** * This interface is used to track changes to the complex data of an * object that implements the StateTrackable interface. * <p> * The usage pattern for code accessing the trackable data is as follows: * <pre> *     StateTrackable trackedobject; *     MyInfo cacheddata; *     StateTracker cachetracker; *     public synchronized MyInfo getInfoAbout(StateTrackable obj) { *         if (trackedobject != obj || !cachetracker.isCurrent()) { *             // Note: Always call getStateTracker() before *             // caching any data about the objct... *             cachetracker = obj.getStateTracker(); *             cacheddata = calculateInfoFrom(obj); *             trackedobject = obj; *         } *         return cacheddata; *     } * </pre> * Note that the sample code above works correctly regardless of the * {@link StateTrackable.State State} of the complex data of the object, * but it may be inefficient to store precalculated information about * an object whose current {@link StateTrackable.State State} is * {@link StateTrackable.State#UNTRACKABLE UNTRACKABLE} * and it is unnecessary to perform the {@link #isCurrent} test for * data whose current {@link StateTrackable.State State} is * {@link StateTrackable.State#IMMUTABLE IMMUTABLE}. * Optimizations to the sample code for either or both of those terminal * States may be of benefit for some use cases, but is left out of the * example to reduce its complexity. * * @see StateTrackable.State * @since 1.7 */public interface StateTracker {    /**     * An implementation of the StateTracker interface which     * always returns true.     * This implementation is useful for objects whose current     * {@link StateTrackable.State State} is     * {@link StateTrackable.State#IMMUTABLE IMMUTABLE}.     * @since 1.7     */    public StateTracker ALWAYS_CURRENT = new StateTracker() {        public boolean isCurrent() {            return true;        }    };     /**     * An implementation of the StateTracker interface which     * always returns false.     * This implementation is useful for objects whose current     * {@link StateTrackable.State State} is     * {@link StateTrackable.State#UNTRACKABLE UNTRACKABLE}.     * This implementation may also be useful for some objects     * whose current {@link StateTrackable.State State} is     * {@link StateTrackable.State#DYNAMIC DYNAMIC}.     * @since 1.7     */    public StateTracker NEVER_CURRENT = new StateTracker() {        public boolean isCurrent() {            return false;        }    };     /**     * Returns true iff the contents of the complex data of the     * associated StateTrackable object have not changed since     * the time that this StateTracker was returned from its     * getStateTracker() method.     * @see StateTrackable     * @since 1.7     */    public boolean isCurrent();}