| /* |
| * Copyright (C) 2011 The Android Open Source Project |
| * |
| * 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 libcore.util; |
| |
| import java.util.LinkedHashMap; |
| import java.util.Map; |
| |
| /** |
| * A minimal least-recently-used cache for libcore. Prefer {@code |
| * android.util.LruCache} where that is available. |
| */ |
| public class BasicLruCache<K, V> { |
| private final LinkedHashMap<K, V> map; |
| private final int maxSize; |
| |
| public BasicLruCache(int maxSize) { |
| if (maxSize <= 0) { |
| throw new IllegalArgumentException("maxSize <= 0"); |
| } |
| this.maxSize = maxSize; |
| this.map = new LinkedHashMap<K, V>(0, 0.75f, true); |
| } |
| |
| /** |
| * Returns the value for {@code key} if it exists in the cache or can be |
| * created by {@code #create}. If a value was returned, it is moved to the |
| * head of the queue. This returns null if a value is not cached and cannot |
| * be created. |
| */ |
| public synchronized final V get(K key) { |
| if (key == null) { |
| throw new NullPointerException(); |
| } |
| |
| V result = map.get(key); |
| if (result != null) { |
| return result; |
| } |
| |
| result = create(key); |
| |
| if (result != null) { |
| map.put(key, result); |
| trimToSize(maxSize); |
| } |
| return result; |
| } |
| |
| /** |
| * Caches {@code value} for {@code key}. The value is moved to the head of |
| * the queue. |
| * |
| * @return the previous value mapped by {@code key}. Although that entry is |
| * no longer cached, it has not been passed to {@link #entryEvicted}. |
| */ |
| public synchronized final V put(K key, V value) { |
| if (key == null || value == null) { |
| throw new NullPointerException(); |
| } |
| |
| V previous = map.put(key, value); |
| trimToSize(maxSize); |
| return previous; |
| } |
| |
| private void trimToSize(int maxSize) { |
| while (map.size() > maxSize) { |
| Map.Entry<K, V> toEvict = map.eldest(); |
| |
| K key = toEvict.getKey(); |
| V value = toEvict.getValue(); |
| map.remove(key); |
| |
| entryEvicted(key, value); |
| } |
| } |
| |
| /** |
| * Called for entries that have reached the tail of the least recently used |
| * queue and are be removed. The default implementation does nothing. |
| */ |
| protected void entryEvicted(K key, V value) {} |
| |
| /** |
| * Called after a cache miss to compute a value for the corresponding key. |
| * Returns the computed value or null if no value can be computed. The |
| * default implementation returns null. |
| */ |
| protected V create(K key) { |
| return null; |
| } |
| |
| /** |
| * Returns a copy of the current contents of the cache, ordered from least |
| * recently accessed to most recently accessed. |
| */ |
| public synchronized final Map<K, V> snapshot() { |
| return new LinkedHashMap<K, V>(map); |
| } |
| |
| /** |
| * Clear the cache, calling {@link #entryEvicted} on each removed entry. |
| */ |
| public synchronized final void evictAll() { |
| trimToSize(0); |
| } |
| } |