Does Java make classes Serializable automatically if used in a Serializable interface?

Question

Let's say I have a Serializable interface as follows

public interface SomeInterface extends Serializable {

     public SomeClass getSomething(String someParameter);

}

Will SomeClass be Serializable automatically? To our surprise, our RMI application runs fine even when SomeClass does not implement Serializable.

Why is this?

Answer 1

Will SomeClass be Serializable automatically? To our surprise, our RMI application runs fine even when SomeClass does not implement Serializable.

No.

Serialization is about serializing the (non-transient) state of an object. The presence of a getSomething in the signature of some method doesn't require the state of your instance of a SomeInterface to include a SomeClass instance.

The method could be implemented to return a newly created SomeClass, the value of a transient field, the result of calling a static method on some other class, or .... null.