001/*
002 * Copyright (C) 2011 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
017package com.google.common.cache;
018
019import com.google.common.annotations.Beta;
020import com.google.common.annotations.GwtCompatible;
021
022/**
023 * An object that can receive a notification when an entry is removed from a cache. The removal
024 * resulting in notification could have occured to an entry being manually removed or replaced, or
025 * due to eviction resulting from timed expiration, exceeding a maximum size, or garbage
026 * collection.
027 *
028 * <p>An instance may be called concurrently by multiple threads to process different entries.
029 * Implementations of this interface should avoid performing blocking calls or synchronizing on
030 * shared resources.
031 *
032 * @param <K> the most general type of keys this listener can listen for; for
033 *     example {@code Object} if any key is acceptable
034 * @param <V> the most general type of values this listener can listen for; for
035 *     example {@code Object} if any key is acceptable
036 * @author Charles Fry
037 * @since 10.0
038 */
039@Beta
040@GwtCompatible
041public interface RemovalListener<K, V> {
042  /**
043   * Notifies the listener that a removal occurred at some point in the past.
044   */
045  // Technically should accept RemovalNotification<? extends K, ? extends V>, but because
046  // RemovalNotification is guaranteed covariant, let's make users' lives simpler.
047  void onRemoval(RemovalNotification<K, V> notification);
048}