@Override
    public boolean deleteFromCache(AssetKey key) {
        return assetCache.remove(key) != null;
    }
A garbage collector bound asset cache that handles non-cloneable objects.
This cache assumes that the asset given to the user is the same asset
that has been stored in the cache, in other words,
{@link AssetProcessor#createClone(java.lang.Object) } for that asset
returns the same object as the argument.
This implementation will remove the asset from the cache
once the asset is no longer referenced in user code and memory is low,
e.g. the VM feels like purging the weak references for that asset.

@author Kirill Vainer
jme3-core/src/main/java/com/jme3/asset/cache/WeakRefAssetCache.java