/*
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* 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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*/
/**
* 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 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 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();
}