Universal-Image-Loader源码阅读（20）-memory/impl/LRULimitedMemoryCache

采用了LRU策略的LimitedMemoryCache

源码：

/**
* Limited {@link Bitmap bitmap} cache. Provides {@link Bitmap bitmaps} storing. Size of all stored bitmaps will not to
* exceed size limit. When cache reaches limit size then the least recently used bitmap is deleted from cache.<br />
* <br />
* <b>NOTE:</b> This cache uses strong and weak references for stored Bitmaps. Strong references - for limited count of
* Bitmaps (depends on cache size), weak references - for all other cached Bitmaps.
*
* @author Sergey Tarasevich (nostra13[at]gmail[dot]com)
* @since 1.3.0
*/
public class LRULimitedMemoryCache extends LimitedMemoryCache {

private static final int INITIAL_CAPACITY = 10;
private static final float LOAD_FACTOR = 1.1f;

/** Cache providing Least-Recently-Used logic */
private final Map<String, Bitmap> lruCache = Collections.synchronizedMap(new LinkedHashMap<String, Bitmap>(INITIAL_CAPACITY, LOAD_FACTOR, true));

/** @param maxSize Maximum sum of the sizes of the Bitmaps in this cache */
public LRULimitedMemoryCache(int maxSize) {
super(maxSize);
}

@Override
public boolean put(String key, Bitmap value) {
if (super.put(key, value)) {
lruCache.put(key, value);
return true;
} else {
return false;
}
}

@Override
public Bitmap get(String key) {
lruCache.get(key); // call "get" for LRU logic
return super.get(key);
}

@Override
public Bitmap remove(String key) {
lruCache.remove(key);
return super.remove(key);
}

@Override
public void clear() {
lruCache.clear();
super.clear();
}

@Override
protected int getSize(Bitmap value) {
return value.getRowBytes() * value.getHeight();
}

@Override
protected Bitmap removeNext() {//关键方法，删除最后的，就是最近最少使用的
Bitmap mostLongUsedValue = null;
synchronized (lruCache) {
Iterator<Entry<String, Bitmap>> it = lruCache.entrySet().iterator();
if (it.hasNext()) {
Entry<String, Bitmap> entry = it.next();
mostLongUsedValue = entry.getValue();
it.remove();
}
}
return mostLongUsedValue;
}

@Override
protected Reference<Bitmap> createReference(Bitmap value) {
return new WeakReference<Bitmap>(value);
}
}