Universal-Image-Loader源码阅读（12）-cache/BaseMemoryCache

作为MemoryCache的第一个实现的抽象类，它主要的共鞥是定义了基本的存储方式--采用弱引用的方法，并且支持多线程的。

源码：

/**
* Base memory cache. Implements common functionality for memory cache. Provides object references (
* {@linkplain Reference not strong}) storing.
*
* @author Sergey Tarasevich (nostra13[at]gmail[dot]com)
* @since 1.0.0
*/
public abstract class BaseMemoryCache implements MemoryCache {

/** Stores not strong references to objects */
private final Map<String, Reference<Bitmap>> softMap = Collections.synchronizedMap(new HashMap<String, Reference<Bitmap>>());

@Override
public Bitmap get(String key) {
Bitmap result = null;
Reference<Bitmap> reference = softMap.get(key);
if (reference != null) {
result = reference.get();
}
return result;
}

@Override
public boolean put(String key, Bitmap value) {
softMap.put(key, createReference(value));
return true;
}

@Override
public Bitmap remove(String key) {
Reference<Bitmap> bmpRef = softMap.remove(key);
return bmpRef == null ? null : bmpRef.get();
}

@Override
public Collection<String> keys() {
synchronized (softMap) {
return new HashSet<String>(softMap.keySet());
}
}

@Override
public void clear() {
softMap.clear();
}

/** Creates {@linkplain Reference not strong} reference of value */
protected abstract Reference<Bitmap> createReference(Bitmap value);
}