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;
20import com.google.common.annotations.GwtCompatible;
21import com.google.common.collect.ImmutableMap;
22import com.google.common.util.concurrent.ExecutionError;
23import com.google.common.util.concurrent.UncheckedExecutionException;
24
25import java.util.Map;
26import java.util.concurrent.Callable;
27import java.util.concurrent.ConcurrentMap;
28import java.util.concurrent.ExecutionException;
29
30import javax.annotation.Nullable;
31
32/**
33 * A semi-persistent mapping from keys to values. Cache entries are manually added using
34 * {@link #get(Object, Callable)} or {@link #put(Object, Object)}, and are stored in the cache until
35 * either evicted or manually invalidated.
36 *
37 * <p>Implementations of this interface are expected to be thread-safe, and can be safely accessed
38 * by multiple concurrent threads.
39 *
40 * <p>Note that while this class is still annotated as {@link Beta}, the API is frozen from a
41 * consumer's standpoint. In other words existing methods are all considered {@code non-Beta} and
42 * won't be changed without going through an 18 month deprecation cycle; however new methods may be
43 * added at any time.
44 *
45 * @author Charles Fry
46 * @since 10.0
47 */
48@Beta
49@GwtCompatible
50public interface Cache<K, V> {
51
52  /**
53   * Returns the value associated with {@code key} in this cache, or {@code null} if there is no
54   * cached value for {@code key}.
55   *
56   * @since 11.0
57   */
58  @Nullable
59  V getIfPresent(Object key);
60
61  /**
62   * Returns the value associated with {@code key} in this cache, obtaining that value from
63   * {@code valueLoader} if necessary. No observable state associated with this cache is modified
64   * until loading completes. This method provides a simple substitute for the conventional
65   * "if cached, return; otherwise create, cache and return" pattern.
66   *
67   * <p><b>Warning:</b> as with {@link CacheLoader#load}, {@code valueLoader} <b>must not</b> return
68   * {@code null}; it may either return a non-null value or throw an exception.
69   *
70   * @throws ExecutionException if a checked exception was thrown while loading the value
71   * @throws UncheckedExecutionException if an unchecked exception was thrown while loading the
72   *     value
73   * @throws ExecutionError if an error was thrown while loading the value
74   *
75   * @since 11.0
76   */
77  V get(K key, Callable<? extends V> valueLoader) throws ExecutionException;
78
79  /**
80   * Returns a map of the values associated with {@code keys} in this cache. The returned map will
81   * only contain entries which are already present in the cache.
82   *
83   * @since 11.0
84   */
85  ImmutableMap<K, V> getAllPresent(Iterable<?> keys);
86
87  /**
88   * Associates {@code value} with {@code key} in this cache. If the cache previously contained a
89   * value associated with {@code key}, the old value is replaced by {@code value}.
90   *
91   * <p>Prefer {@link #get(Object, Callable)} when using the conventional "if cached, return;
92   * otherwise create, cache and return" pattern.
93   *
94   * @since 11.0
95   */
96  void put(K key, V value);
97
98  /**
99   * Copies all of the mappings from the specified map to the cache. The effect of this call is
100   * equivalent to that of calling {@code put(k, v)} on this map once for each mapping from key
101   * {@code k} to value {@code v} in the specified map. The behavior of this operation is undefined
102   * if the specified map is modified while the operation is in progress.
103   *
104   * @since 12.0
105   */
106  void putAll(Map<? extends K,? extends V> m);
107
108  /**
109   * Discards any cached value for key {@code key}.
110   */
111  void invalidate(Object key);
112
113  /**
114   * Discards any cached values for keys {@code keys}.
115   *
116   * @since 11.0
117   */
118  void invalidateAll(Iterable<?> keys);
119
120  /**
121   * Discards all entries in the cache.
122   */
123  void invalidateAll();
124
125  /**
126   * Returns the approximate number of entries in this cache.
127   */
128  long size();
129
130  /**
131   * Returns a current snapshot of this cache's cumulative statistics. All stats are initialized
132   * to zero, and are monotonically increasing over the lifetime of the cache.
133   *
134   */
135  CacheStats stats();
136
137  /**
138   * Returns a view of the entries stored in this cache as a thread-safe map. Modifications made to
139   * the map directly affect the cache.
140   *
141   * <p>Iterators from the returned map are at least <i>weakly consistent</i>: they are safe for
142   * concurrent use, but if the cache is modified (including by eviction) after the iterator is
143   * created, it is undefined which of the changes (if any) will be reflected in that iterator.
144   */
145  ConcurrentMap<K, V> asMap();
146
147  /**
148   * Performs any pending maintenance operations needed by the cache. Exactly which activities are
149   * performed -- if any -- is implementation-dependent.
150   */
151  void cleanUp();
152}
153