org.apache.wicket.util.collections.MostRecentlyUsedMap Maven / Gradle / Ivy
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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.
*/
package org.apache.wicket.util.collections;
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
* @param
* key type
* @param
* value type
*/
public class MostRecentlyUsedMap extends LinkedHashMap
{
private static final long serialVersionUID = 1L;
/** Value most recently removed from map */
protected V removedValue;
/** Maximum number of entries allowed in this map */
private final 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 V getRemovedValue()
{
return removedValue;
}
/**
* @see java.util.LinkedHashMap#removeEldestEntry(java.util.Map.Entry)
*/
@Override
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;
}
}