com.github.marcosalis.kraken.cache.ContentLruCache.java Source code

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Here is the source code for com.github.marcosalis.kraken.cache.ContentLruCache.java

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/*
 * Copyright 2013 Luluvise Ltd
 * Copyright 2013 Marco Salis - fast3r(at)gmail.com
 *
 * 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.github.marcosalis.kraken.cache;

import java.util.concurrent.ConcurrentMap;

import javax.annotation.CheckForNull;
import javax.annotation.Nonnegative;
import javax.annotation.Nonnull;
import javax.annotation.OverridingMethodsMustInvokeSuper;

import android.support.v4.util.LruCache;

import com.google.common.annotations.Beta;
import com.google.common.cache.Cache;

/**
 * Extension of the Android's {@link LruCache} to support some of the methods of
 * a {@link ConcurrentMap}.
 * 
 * TODO: unit tests
 * 
 * TODO: use Guava's {@link Cache} instead? It's really concurrent (backed by a
 * ConcurrentHashMap implementation, whereas LruCache operations block on the
 * whole structure) and automatically handles blocking load with Future's get().
 * 
 * @since 1.0
 * @author Marco Salis
 */
@Beta
public class ContentLruCache<K, V> extends LruCache<K, V> implements MemoryCache<K, V> {

    @SuppressWarnings("unused")
    private static final String TAG = ContentLruCache.class.getSimpleName();

    public ContentLruCache(@Nonnegative int maxSize) {
        super(maxSize);
    }

    /**
     * If the specified key is not already associated with a value, associate it
     * with the given value.
     * 
     * @param key
     *            key with which the specified value is to be associated
     * @param value
     *            value to be associated with the specified key
     * @return the previous value associated with the specified key, or null if
     *         there was no mapping for the key. (A null return can also
     *         indicate that the map previously associated null with the key, if
     *         the implementation supports null values.)
     */
    @CheckForNull
    public synchronized V putIfAbsent(@Nonnull K key, V value) {
        V old = null;
        if ((old = get(key)) == null) {
            return put(key, value);
        } else {
            return old;
        }
    }

    /**
     * Remove a cache entry if the key is currently associated with the passed
     * object.
     * 
     * @param key
     * @param value
     * @return true if the element was removed, false otherwise
     */
    public boolean remove(@Nonnull K key, V value) {
        if (value == null) {
            return false;
        }
        synchronized (this) {
            V oldValue = get(key);
            if (oldValue != null && oldValue.equals(value)) {
                remove(key);
                return true;
            }
            return false;
        }
    }

    @Override
    @OverridingMethodsMustInvokeSuper
    public void clear() {
        evictAll();
    }

    /**
     * @throws UnsupportedOperationException
     */
    @Override
    public void setOnEntryRemovedListener(OnEntryRemovedListener<K, V> listener) {
        throw new UnsupportedOperationException();
    }

}