com.hazelcast.map.eviction.MapEvictionPolicy Maven / Gradle / Ivy
/*
* Copyright (c) 2008-2018, Hazelcast, Inc. All Rights Reserved.
*
* 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 com.hazelcast.map.eviction;
import com.hazelcast.core.EntryView;
import java.util.Comparator;
/**
* An eviction policy takes its role after the decision that a map needs to free some memory
* according to one of {@link com.hazelcast.config.MaxSizeConfig.MaxSizePolicy MaxSizePolicies}
* and it helps to find most appropriate entries to remove.
*
* {@link com.hazelcast.core.IMap IMap} has out-of-the-box eviction policies like {@link LRUEvictionPolicy},
* {@link LFUEvictionPolicy} and {@link RandomEvictionPolicy} but if there is a need to define another eviction policy,
* users can introduce a custom one by extending {@link MapEvictionPolicy} class.
*
* Implementation:
* {@link MapEvictionPolicy#compare(EntryView, EntryView)} method must be implemented to provide an ascending order
* of entries. Because internal eviction algorithm will evict the smallest entry from {@link com.hazelcast.core.IMap IMap}
*
* @param the type of keys maintained by IMap
* @param the type of mapped values
*
* @see LRUEvictionPolicy
* @see LFUEvictionPolicy
* @see RandomEvictionPolicy
*
* @since 3.7
*/
public abstract class MapEvictionPolicy implements Comparator> {
/**
* {@inheritDoc}
*
*
* If you prefer to evict the 1st entry then return negative number, if the 2nd entry is a better candidate
* then return a positive number or return 0 if both entries are equally good candidates for eviction
*
*/
@Override
public abstract int compare(EntryView entryView1, EntryView entryView2);
}