001    /*
002     * Copyright (C) 2010 The Guava Authors
003     *
004     * Licensed under the Apache License, Version 2.0 (the "License");
005     * you may not use this file except in compliance with the License.
006     * You may obtain a copy of the License at
007     *
008     * http://www.apache.org/licenses/LICENSE-2.0
009     *
010     * Unless required by applicable law or agreed to in writing, software
011     * distributed under the License is distributed on an "AS IS" BASIS,
012     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013     * See the License for the specific language governing permissions and
014     * limitations under the License.
015     */
016    
017    package com.google.common.collect;
018    
019    import com.google.common.annotations.Beta;
020    
021    import javax.annotation.Nullable;
022    
023    /**
024     * An object that can receive a notification when an entry is evicted from a
025     * map.
026     *
027     * <p>An instance may be called concurrently by multiple threads to process
028     * different entries. Implementations of this interface should avoid performing
029     * blocking calls or synchronizing on shared resources.
030     *
031     * @param <K> the type of keys being evicted
032     * @param <V> the type of values being evicted
033     * @author Ben Manes
034     * @since 7
035     */
036    @Beta
037    public interface MapEvictionListener<K, V> {
038    
039      /**
040       * Notifies the listener that an eviction has occurred. Eviction may be for
041       * reasons such as timed expiration, exceeding a maximum size, or due to
042       * garbage collection. Eviction notification does <i>not</i> occur due to
043       * manual removal.
044       *
045       * @param key the key of the entry that has already been evicted, or {@code
046       *     null} if its reference was collected
047       * @param value the value of the entry that has already been evicted, or
048       *     {@code null} if its reference was collected
049       */
050      void onEviction(@Nullable K key, @Nullable V value);
051    }