Additional -Xlint:serial warning

Neal Gafter neal at
Wed Aug 4 08:14:27 PDT 2010

Unfortunately, many inner classes are only "incidentally" serializable -
that is, they are serializable because the superclass or some implemented
interface extends Serializable.  A simple example would be an inner
exception class - even though most programs do not serialize exceptions,
this would trigger the proposed diagnostic.

On Wed, Aug 4, 2010 at 4:50 AM, Florian Weimer <fweimer at> wrote:

> The JLS does not provide binary compatibility for compiler-generated
> fields (such as reference to an outer class object from an inner class
> object).  This means that there is no reliable way to use such classes
> in serialization even if all involved classes implement
>  A mere recompilation of unchanged sources might
> result in different compiler-generated names.
> Would it make sense to enhance -Xlint:serial to warn about classes
> which implement and contain compiler-generated
> fields?
> PS: This is quite different from the frequently observed issue where a
> non-static inner class cannot be serialized because the outer class is
> not serializable.  Serialization works fine, but deserialization
> silently results in invalid objects.
> --
> Florian Weimer                <fweimer at>
> BFK edv-consulting GmbH
> Kriegsstraße 100              tel: +49-721-96201-1
> D-76133 Karlsruhe             fax: +49-721-96201-99
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