| Class | Description | 
|---|---|
| ApplicationVersionSignature | A utility class for obtaining a  Keysignature containing the
 application version name usingPackageInfo.versionCode. | 
| EmptySignature | An empty key that is always equal to all other empty keys. | 
| MediaStoreSignature | A unique signature based on metadata data from the media store that detects common changes to
 media store files like edits, rotations, and temporary file replacement. | 
| ObjectKey | Wraps an  Object, delegatingObjectKey.equals(Object)andObjectKey.hashCode()to
 the wrapped Object and providing the bytes of the result of the Object'sObjectKey.toString()method to theMessageDigestinObjectKey.updateDiskCacheKey(java.security.MessageDigest). |