Why is it legal to declare a transient variable in a non serializable class?

Question

As for the subject title: Why is it legal to declare a transient variable in a non serializable class? What would the use be?

Answer 1

The transient access modifier can be seen by code other than the serialization mechanism, and is used by some object databases to mark a data field as not persistent. Aside from that, there isn't any harm in allowing this.

Answer 2

Because also other serialization forms that don't requirier Serializable are able to make use of it too.

Answer 3

How about if a subclass implements Serializable?

In any case, it is impossible for the compiler to enforce this rule, i.e. emit a compile error
based on class hierarchy (except - of course - superclass defined methods).