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