Mega Code Archive
Most Recently Used Map
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/*
* $Id: MostRecentlyUsedMap.java 457812 2005-10-06 21:20:34Z jdonnerstag $
* $Revision: 457812 $ $Date: 2005-10-06 23:20:34 +0200 (Thu, 06 Oct 2005) $
*
*
* Licensed under the Apache License, Version 2.0 (the "License"); you may not
* use this file except in compliance with the License. You may obtain a copy of
* the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations under
* the License.
*/
import java.util.LinkedHashMap;
import java.util.Map;
/**
* Holds a map of most recently used items of a given maximum size. Old entries
* are expired when the map exceeds that maximum size.
*
* @author Jonathan Locke
*/
public class MostRecentlyUsedMap extends LinkedHashMap
{
private static final long serialVersionUID = 1L;
/** Value most recently removed from map */
Object removedValue;
/** Maximum number of entries allowed in this map */
private int maxEntries;
/**
* Constructor
*
* @param maxEntries
* Maximum number of entries allowed in the map
*/
public MostRecentlyUsedMap(final int maxEntries)
{
super(10, 0.75f, true);
if (maxEntries <= 0)
{
throw new IllegalArgumentException("Must have at least one entry");
}
this.maxEntries = maxEntries;
}
/**
* @return Returns the removedValue.
*/
public Object getRemovedValue()
{
return removedValue;
}
/**
* @see java.util.LinkedHashMap#removeEldestEntry(java.util.Map.Entry)
*/
protected boolean removeEldestEntry(final Map.Entry eldest)
{
final boolean remove = size() > maxEntries;
// when it should be removed remember the oldest value that will be removed
if (remove)
{
this.removedValue = eldest.getValue();
}
else
{
removedValue = null;
}
return remove;
}
}
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