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      1 /*
      2  * Copyright (C) 2009 The Android Open Source Project
      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 
     17 package com.android.camera.gallery;
     18 
     19 import java.lang.ref.ReferenceQueue;
     20 import java.lang.ref.WeakReference;
     21 import java.util.HashMap;
     22 import java.util.LinkedHashMap;
     23 import java.util.Map;
     24 
     25 public class LruCache<K, V> {
     26 
     27     private final HashMap<K, V> mLruMap;
     28     private final HashMap<K, Entry<K, V>> mWeakMap =
     29             new HashMap<K, Entry<K, V>>();
     30     private ReferenceQueue<V> mQueue = new ReferenceQueue<V>();
     31 
     32     @SuppressWarnings("serial")
     33     public LruCache(final int capacity) {
     34         mLruMap = new LinkedHashMap<K, V>(16, 0.75f, true) {
     35             @Override
     36             protected boolean removeEldestEntry(Map.Entry<K, V> eldest) {
     37                 return size() > capacity;
     38             }
     39         };
     40     }
     41 
     42     private static class Entry<K, V> extends WeakReference<V> {
     43         K mKey;
     44 
     45         public Entry(K key, V value, ReferenceQueue<V> queue) {
     46             super(value, queue);
     47             mKey = key;
     48         }
     49     }
     50 
     51     @SuppressWarnings("unchecked")
     52     private void cleanUpWeakMap() {
     53         Entry<K, V> entry = (Entry<K, V>) mQueue.poll();
     54         while (entry != null) {
     55             mWeakMap.remove(entry.mKey);
     56             entry = (Entry<K, V>) mQueue.poll();
     57         }
     58     }
     59 
     60     public synchronized V put(K key, V value) {
     61         cleanUpWeakMap();
     62         mLruMap.put(key, value);
     63         Entry<K, V> entry = mWeakMap.put(
     64                 key, new Entry<K, V>(key, value, mQueue));
     65         return entry == null ? null : entry.get();
     66     }
     67 
     68     public synchronized V get(K key) {
     69         cleanUpWeakMap();
     70         V value = mLruMap.get(key);
     71         if (value != null) return value;
     72         Entry<K, V> entry = mWeakMap.get(key);
     73         return entry == null ? null : entry.get();
     74     }
     75 
     76     public synchronized void clear() {
     77         mLruMap.clear();
     78         mWeakMap.clear();
     79         mQueue = new ReferenceQueue<V>();
     80     }
     81 }
     82