AbstractMessage
A partial implementation of the Message interface which implements
as many methods of that interface as possible in terms of other methods.
AbstractMessageLite
A partial implementation of the MessageLite interface which
implements as many methods of that interface as possible in terms of other
methods.
UnknownFieldSet UnknownFieldSet is used to keep track of fields which were seen when
parsing a protocol message but whose field numbers or types are unrecognized.