JDK for Solaris Developer's Guide

Serialization

Support has been added to handle enumerated types which are new in version 1.5.0. The rules for serializing an enum instance differ from those for serializing an ordinary serializable object: the serialized form of an enum instance consists only of its enum constant name, along with information identifying its base enum type. Deserialization behavior differs as well--the class information is used to find the appropriate enum class, and the Enum.valueOf method is called with that class and the received constant name in order to obtain the enum constant to return.

Refer to the documentation at http://java.sun.com/j2se/1.5.0/docs/guide/serialization/index.html.