/*

 * 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

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 */

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();

}