JavaMemoryModel: Serialization and final fields

From: Bill Pugh (
Date: Tue Aug 24 1999 - 23:42:25 EDT

I starting thinking about the semantics of serialization and final
fields; it is ugly.

When an object is being restored from a serialized form, the
constructor that would normally set the final fields isn't called.
Instead, the value of the final field is set by the de-serialization

Some questions/issues:
   * It is apparent that the defaultReadObject function can set final fields.
It would seem that if you
        - used your own readObject method (without calling defaultReadObject),
        - used serialPersistentFields
        - used the Externalizable interface
it is _impossible_ to set final fields. Does anyone disagree? This
might prove to be a drawback to using final to handle the
immutability problem; sometimes you can't use it because you want to
have your own custom Serialization scheme.

   * Whatever special status we grant to constructors and/or final
fields (if any) should (in my opinion) also apply to instances that
have been de-serialized. Which means that we are going to need to
talk about defaultReadObject and readObject in the formal
specification of the memory model. Yuck!


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