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.base.Function;
22import com.google.common.collect.ImmutableMap;
23import com.google.common.util.concurrent.ExecutionError;
24import com.google.common.util.concurrent.UncheckedExecutionException;
25
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(K, Callable)} or {@link #put(K, V)}, and are stored in the cache until either
35 * evicted or manually invalidated.
36 *
37 * <p><b>Note:</b> in release 12.0, all methods moved from {@code Cache} to {@link LoadingCache}
38 * will be deleted from {@code Cache}. As part of this transition {@code Cache} will no longer
39 * extend {@link Function}.
40 *
41 * <p>Implementations of this interface are expected to be thread-safe, and can be safely accessed
42 * by multiple concurrent threads.
43 *
44 * <p>All methods other than {@link #getIfPresent} are optional.
45 *
46 * @author Charles Fry
47 * @since 10.0
48 */
49@Beta
50@GwtCompatible
51public interface Cache<K, V> extends Function<K, V> {
52
53  /**
54   * Returns the value associated with {@code key} in this cache, or {@code null} if there is no
55   * cached value for {@code key}.
56   *
57   * @since 11.0
58   */
59  @Nullable
60  V getIfPresent(K key);
61
62  /**
63   * Returns the value associated with {@code key} in this cache, obtaining that value from
64   * {@code valueLoader} if necessary. No observable state associated with this cache is modified
65   * until loading completes. This method provides a simple substitute for the conventional
66   * "if cached, return; otherwise create, cache and return" pattern.
67   *
68   * <p><b>Warning:</b> as with {@link CacheLoader#load}, {@code valueLoader} <b>must not</b> return
69   * {@code null}; it may either return a non-null value or throw an exception.
70   *
71   * @throws ExecutionException if a checked exception was thrown while loading the value
72   * @throws UncheckedExecutionException if an unchecked exception was thrown while loading the
73   *     value
74   * @throws ExecutionError if an error was thrown while loading the value
75   *
76   * @since 11.0
77   */
78  V get(K key, Callable<? extends V> valueLoader) throws ExecutionException;
79
80  /**
81   * Returns a map of the values associated with {@code keys} in this cache. The returned map will
82   * only contain entries which are already present in the cache.
83   *
84   * @since 11.0
85   */
86  ImmutableMap<K, V> getAllPresent(Iterable<? extends K> keys);
87
88  /**
89   * Associates {@code value} with {@code key} in this cache. If the cache previously contained a
90   * value associated with {@code key}, the old value is replaced by {@code value}.
91   *
92   * <p>Prefer {@link #get(Object, Callable)} when using the conventional "if cached, return;
93   * otherwise create, cache and return" pattern.
94   *
95   * @since 11.0
96   */
97  void put(K key, V value);
98
99  /**
100   * Discards any cached value for key {@code key}.
101   */
102  void invalidate(Object key);
103
104  /**
105   * Discards any cached values for keys {@code keys}.
106   *
107   * @since 11.0
108   */
109  void invalidateAll(Iterable<?> keys);
110
111  /**
112   * Discards all entries in the cache.
113   */
114  void invalidateAll();
115
116  /**
117   * Returns the approximate number of entries in this cache.
118   */
119  long size();
120
121  /**
122   * Returns a current snapshot of this cache's cumulative statistics. All stats are initialized
123   * to zero, and are monotonically increasing over the lifetime of the cache.
124   */
125  CacheStats stats();
126
127  /**
128   * Returns a view of the entries stored in this cache as a thread-safe map. Modifications made to
129   * the map directly affect the cache.
130   */
131  ConcurrentMap<K, V> asMap();
132
133  /**
134   * Performs any pending maintenance operations needed by the cache. Exactly which activities are
135   * performed -- if any -- is implementation-dependent.
136   */
137  void cleanUp();
138
139  /**
140   * Returns the value associated with {@code key} in this cache, first loading that value if
141   * necessary. No observable state associated with this cache is modified until loading completes.
142   *
143   * @throws ExecutionException if a checked exception was thrown while loading the value
144   * @throws UncheckedExecutionException if an unchecked exception was thrown while loading the
145   *     value
146   * @throws ExecutionError if an error was thrown while loading the value
147   * @deprecated This method has been split out into the {@link LoadingCache} interface, and will be
148   * removed from {@code Cache} in Guava release 12.0. Note that
149   * {@link CacheBuilder#build(CacheLoader)} now returns a {@code LoadingCache}, so this deprecation
150   * (migration) can be dealt with by simply changing the type of references to the results of
151   * {@link CacheBuilder#build(CacheLoader)}.
152   */
153  @Deprecated V get(K key) throws ExecutionException;
154
155  /**
156   * Returns the value associated with {@code key} in this cache, first loading that value if
157   * necessary. No observable state associated with this cache is modified until computation
158   * completes. Unlike {@link #get}, this method does not throw a checked exception, and thus should
159   * only be used in situations where checked exceptions are not thrown by the cache loader.
160   *
161   * <p><b>Warning:</b> this method silently converts checked exceptions to unchecked exceptions,
162   * and should not be used with cache loaders which throw checked exceptions.
163   *
164   * @throws UncheckedExecutionException if an exception was thrown while loading the value,
165   *     regardless of whether the exception was checked or unchecked
166   * @throws ExecutionError if an error was thrown while loading the value
167   * @deprecated This method has been split out into the {@link LoadingCache} interface, and will be
168   * removed from {@code Cache} in Guava release 12.0. Note that
169   * {@link CacheBuilder#build(CacheLoader)} now returns a {@code LoadingCache}, so this deprecation
170   * (migration) can be dealt with by simply changing the type of references to the results of
171   * {@link CacheBuilder#build(CacheLoader)}.
172   */
173  @Deprecated V getUnchecked(K key);
174
175  /**
176   * Discouraged. Provided to satisfy the {@code Function} interface; use {@link #get} or
177   * {@link #getUnchecked} instead.
178   *
179   * @throws UncheckedExecutionException if an exception was thrown while loading the value,
180   *     regardless of whether the exception was checked or unchecked
181   * @throws ExecutionError if an error was thrown while loading the value
182   * @deprecated This method has been split out into the {@link LoadingCache} interface, and will be
183   * removed from {@code Cache} in Guava release 12.0. Note that
184   * {@link CacheBuilder#build(CacheLoader)} now returns a {@code LoadingCache}, so this deprecation
185   * (migration) can be dealt with by simply changing the type of references to the results of
186   * {@link CacheBuilder#build(CacheLoader)}.
187   */
188  @Deprecated V apply(K key);
189}
190