org.apache.flink.table.util.LRUMap Maven / Gradle / Ivy
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* 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.flink.table.util;
import java.util.LinkedHashMap;
import java.util.Map;
/**
* An LRU cache, based on LinkedHashMap.
*
* This cache has a fixed maximum number of elements (cacheSize).
* If the cache is full and another entry is added, the LRU (least recently
* used) entry is dropped.
*
*
Note: This class is not thread-safe.
*/
public class LRUMap extends LinkedHashMap {
private static final long serialVersionUID = 6148230381293590639L;
private final int cacheSize;
private final RemovalListener removalListener;
public LRUMap(int cacheSize) {
this(cacheSize, null);
}
public LRUMap(int cacheSize, RemovalListener removalListener) {
super((int) Math.ceil(cacheSize / 0.75) + 1, 0.75F, true);
this.cacheSize = cacheSize;
this.removalListener = removalListener;
}
protected boolean removeEldestEntry(Map.Entry eldest) {
if (size() > cacheSize) {
if (removalListener != null) {
removalListener.onRemoval(eldest);
}
return true;
} else {
return false;
}
}
/**
* An object that can receive a notification when an entry is removed from a LRUMap.
* @param the type of keys maintained by this map
* @param the type of mapped values
*/
public interface RemovalListener {
void onRemoval(Map.Entry eldest);
}
}