1/*
2 * Copyright (C) 2011 The Guava Authors
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17package com.google.common.cache;
18
19import com.google.common.annotations.Beta;
20
21/**
22 * An object that can receive a notification when an entry is removed from a cache. The removal
23 * resulting in notification could have occured to an entry being manually removed or replaced, or
24 * due to eviction resulting from timed expiration, exceeding a maximum size, or garbage
25 * collection.
26 *
27 * <p>An instance may be called concurrently by multiple threads to process different entries.
28 * Implementations of this interface should avoid performing blocking calls or synchronizing on
29 * shared resources.
30 *
31 * @param <K> the most general type of keys this listener can listen for; for
32 *     example {@code Object} if any key is acceptable
33 * @param <V> the most general type of values this listener can listen for; for
34 *     example {@code Object} if any key is acceptable
35 * @author Charles Fry
36 * @since 10.0
37 */
38@Beta
39public interface RemovalListener<K, V> {
40  /**
41   * Notifies the listener that a removal occurred at some point in the past.
42   */
43  // Technically should accept RemovalNotification<? extends K, ? extends V>, but because
44  // RemovalNotification is guaranteed covariant, let's make users' lives simpler.
45  void onRemoval(RemovalNotification<K, V> notification);
46}
47