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/**
 *  Copyright Terracotta, Inc.
 *
 *  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.
 */

package net.sf.ehcache.store;

import net.sf.ehcache.Element;

/**
 * An eviction policy.
 * 

* The Cache will use a policy at startup. There are three policy implementations provided in ehcache: * LRU, LFU and FIFO. However many other policies are possible. That the policy * has access to the whole element enables policies based on the key, value, metadata, statistics, or a combination of * any of the above. * * @author Greg Luck */ public interface Policy { /** * @return the name of the Policy. Inbuilt examples are LRU, LFU and FIFO. */ String getName(); /** * Finds the best eviction candidate based on the sampled elements. What distinguishes * this approach from the classic data structures approach is that an Element contains * metadata (e.g. usage statistics) which can be used for making policy decisions, * while generic data structures do not. It is expected that implementations will take * advantage of that metadata. * * @param sampledElements this should be a random subset of the population * @param justAdded we probably never want to select the element just added. * It is provided so that it can be ignored if selected. May be null. * @return the selected Element */ Element selectedBasedOnPolicy(Element[] sampledElements, Element justAdded); /** * Compares the desirableness for eviction of two elements * * @param element1 the element to compare against * @param element2 the element to compare * @return true if the second element is preferable for eviction to the first element * under ths policy */ boolean compare(Element element1, Element element2); }





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