LruCache.java

/** 
    Copyright 2015 Tim Engler, Rareventure LLC

    This file is part of Tiny Travel Tracker.

    Tiny Travel Tracker is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    Tiny Travel Tracker is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with Tiny Travel Tracker.  If not, see <http://www.gnu.org/licenses/>.

*/
/*
 * Copyright (C) 2009 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 com.rareventure.gps2.reviewer.imageviewer;

import java.lang.ref.ReferenceQueue;
import java.lang.ref.WeakReference;
import java.util.HashMap;
import java.util.LinkedHashMap;
import java.util.Map;

public class LruCache<K, V> {

    private final HashMap<K, V> mLruMap;
    private final HashMap<K, Entry<K, V>> mWeakMap =
            new HashMap<K, Entry<K, V>>();
    private ReferenceQueue<V> mQueue = new ReferenceQueue<V>();

    @SuppressWarnings("serial")
    public LruCache(final int capacity) {
        mLruMap = new LinkedHashMap<K, V>(16, 0.75f, true) {
            @Override
            protected boolean removeEldestEntry(Map.Entry<K, V> eldest) {
                return size() > capacity;
            }
        };
    }

    private static class Entry<K, V> extends WeakReference<V> {
        K mKey;

        public Entry(K key, V value, ReferenceQueue<V> queue) {
            super(value, queue);
            mKey = key;
        }
    }

    @SuppressWarnings("unchecked")
    private void cleanUpWeakMap() {
        Entry<K, V> entry = (Entry<K, V>) mQueue.poll();
        while (entry != null) {
            mWeakMap.remove(entry.mKey);
            entry = (Entry<K, V>) mQueue.poll();
        }
    }

    public synchronized V put(K key, V value) {
        cleanUpWeakMap();
        mLruMap.put(key, value);
        Entry<K, V> entry = mWeakMap.put(
                key, new Entry<K, V>(key, value, mQueue));
        return entry == null ? null : entry.get();
    }

    public synchronized V get(K key) {
        cleanUpWeakMap();
        V value = mLruMap.get(key);
        if (value != null) return value;
        Entry<K, V> entry = mWeakMap.get(key);
        return entry == null ? null : entry.get();
    }

    public synchronized void clear() {
        mLruMap.clear();
        mWeakMap.clear();
        mQueue = new ReferenceQueue<V>();
    }
}