CacheMap.java

/*
 * Copyright 2015 S. Webber
 *
 * 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 org.oakgp.util;

import java.util.Collections;
import java.util.LinkedHashMap;
import java.util.Map;

/**
 * Provides a size-limited map of keys to values.
 * <p>
 * When the maximum size limit has been reached, the least-recently accessed entry will be removed whenever a new entry is added.
 *
 * @param <K>
 *           the type of keys maintained by this map
 * @param <V>
 *           the type of mapped values
 */
public final class CacheMap<K, V> extends LinkedHashMap<K, V> {
   private static final long serialVersionUID = 1L;

   private final int maxSize;

   /**
    * Returns a size-limited map of keys to values.
    *
    * @param maxSize
    *           the maximum size restriction to enforce on the returned map
    * @param <K>
    *           the type of keys maintained by this map
    * @param <V>
    *           the type of mapped values
    * @return a size-limited map of keys to values
    */
   public static <K, V> Map<K, V> createCache(int maxSize) {
      CacheMap<K, V> m = new CacheMap<>(maxSize);
      return Collections.synchronizedMap(m);
   }

   /**
    * @param maxSize
    *           the maximum size restriction to enforce on the returned map
    * @see #createCache(int)
    */
   private CacheMap(int maxSize) {
      super(maxSize, 0.1f, true);
      this.maxSize = maxSize;
   }

   @Override
   protected boolean removeEldestEntry(Map.Entry<K, V> eldest) {
      return size() > maxSize;
   }
}