This class is intended to TAG immutable serializable classes.
When you have too identical user immutable classes in a serialization graph tree, they will be considered as a single entity
and reading the object tree would cause a single object reference also.
This is useful if for example you are serializing an object read from the database, and you have several identical instances
on the tree. They will be all considered a single instance and JBossSerialziation will place then as references.
Classes implementing Immutable are required to provide a proper equals and a proper hashCode implementations.