com.google.common.cache.Cache.java Source code

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Here is the source code for com.google.common.cache.Cache.java

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/*
 * Copyright (C) 2011 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.cache;

import com.google.common.annotations.GwtCompatible;
import com.google.common.collect.ImmutableMap;
import com.google.common.util.concurrent.ExecutionError;
import com.google.common.util.concurrent.UncheckedExecutionException;

import java.util.Map;
import java.util.concurrent.Callable;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.ExecutionException;

import javax.annotation.Nullable;

/**
 * A semi-persistent mapping from keys to values. Cache entries are manually added using
 * {@link #get(Object, Callable)} or {@link #put(Object, Object)}, and are stored in the cache until
 * either evicted or manually invalidated.
 *
 * <p>Implementations of this interface are expected to be thread-safe, and can be safely accessed
 * by multiple concurrent threads.
 *
 * @author Charles Fry
 * @since 10.0
 */
@GwtCompatible
public interface Cache<K, V> {

    /**
     * Returns the value associated with {@code key} in this cache, or {@code null} if there is no
     * cached value for {@code key}.
     *
     * @since 11.0
     */
    @Nullable
    V getIfPresent(Object key);

    /**
     * Returns the value associated with {@code key} in this cache, obtaining that value from
     * {@code valueLoader} if necessary. No observable state associated with this cache is modified
     * until loading completes. This method provides a simple substitute for the conventional
     * "if cached, return; otherwise create, cache and return" pattern.
     *
     * <p><b>Warning:</b> as with {@link CacheLoader#load}, {@code valueLoader} <b>must not</b> return
     * {@code null}; it may either return a non-null value or throw an exception.
     *
     * @throws ExecutionException if a checked exception was thrown while loading the value
     * @throws UncheckedExecutionException if an unchecked exception was thrown while loading the
     *     value
     * @throws ExecutionError if an error was thrown while loading the value
     *
     * @since 11.0
     */
    V get(K key, Callable<? extends V> valueLoader) throws ExecutionException;

    /**
     * Returns a map of the values associated with {@code keys} in this cache. The returned map will
     * only contain entries which are already present in the cache.
     *
     * @since 11.0
     */
    ImmutableMap<K, V> getAllPresent(Iterable<?> keys);

    /**
     * Associates {@code value} with {@code key} in this cache. If the cache previously contained a
     * value associated with {@code key}, the old value is replaced by {@code value}.
     *
     * <p>Prefer {@link #get(Object, Callable)} when using the conventional "if cached, return;
     * otherwise create, cache and return" pattern.
     *
     * @since 11.0
     */
    void put(K key, V value);

    /**
     * Copies all of the mappings from the specified map to the cache. The effect of this call is
     * equivalent to that of calling {@code put(k, v)} on this map once for each mapping from key
     * {@code k} to value {@code v} in the specified map. The behavior of this operation is undefined
     * if the specified map is modified while the operation is in progress.
     *
     * @since 12.0
     */
    void putAll(Map<? extends K, ? extends V> m);

    /**
     * Discards any cached value for key {@code key}.
     */
    void invalidate(Object key);

    /**
     * Discards any cached values for keys {@code keys}.
     *
     * @since 11.0
     */
    void invalidateAll(Iterable<?> keys);

    /**
     * Discards all entries in the cache.
     */
    void invalidateAll();

    /**
     * Returns the approximate number of entries in this cache.
     */
    long size();

    /**
     * Returns a current snapshot of this cache's cumulative statistics. All stats are initialized
     * to zero, and are monotonically increasing over the lifetime of the cache.
     *
     */
    CacheStats stats();

    /**
     * Returns a view of the entries stored in this cache as a thread-safe map. Modifications made to
     * the map directly affect the cache.
     *
     * <p>Iterators from the returned map are at least <i>weakly consistent</i>: they are safe for
     * concurrent use, but if the cache is modified (including by eviction) after the iterator is
     * created, it is undefined which of the changes (if any) will be reflected in that iterator.
     */
    ConcurrentMap<K, V> asMap();

    /**
     * Performs any pending maintenance operations needed by the cache. Exactly which activities are
     * performed -- if any -- is implementation-dependent.
     */
    void cleanUp();
}