Re: Object implements Serializable, but includes field(s) that do NOT implement Serializable

Thomas Hawtin <>
Wed, 08 Aug 2007 13:22:00 +0100
Zig wrote:

Excerpt from

"Serialization does not write out the fields of any object that does not
implement the interface. Subclasses of Objects that
are not serializable can be serializable. In this case the
non-serializable class must have a no-arg constructor to allow its
fields to be initialized. In this case it is the responsibility of the
subclass to save and restore the state of the non-serializable class. It
is frequently the case that the fields of that class are accessible
(public, package, or protected) or that there are get and set methods
that can be used to restore the state."

Now, I generally recommend checking that subtypes all implement
Serializable where necessary, but this suggests that the field ghiObject
should be ok if either: ghiObject is a subclass of GHI and implement
sSerializable/Externalizable, or ghiObject is a class that has a public
no-arg constructor which will leave the object in a suitable state.

It requires *both*:

  * The class implement Serializable somewhere along the line.

  * The first non-serializable subclass have a no-arg constructor. In
the example, there is absolutely no need for this to be GHI. Indeed, it
can be necessary to introduce an intermediate subclass purely to provide
the no-arg constructor.

It's appears to be common to believe that serializable classes need
no-args constructors. This is not the case.

Tom Hawtin

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