Guava ForwardingObject, Serializable and parameterless constructor

Question

From the javadoc of guava's ForwardingObject:

Although this class does not implement Serializable, a serializable subclass may be created since this class has a parameter-less constructor.

Why is a parameterless constructor needed for a class to be able to be Serializable? Am I misunderstanding something, or is this just an error in the javadoc?

Answer 1

It just means you can write:

class MyForwardingFoo extends ForwardingObject implements Serializable {
  //
}

and it'll be serializable despite ForwardingObject itself isn't serializable; mentioning empty constructor isn't probably the best wording there but from the language perspective it's a sufficient condition to achieve serializability. What's more important is the fact that ForwardingObject itself doesn't hold any non-serializable fields.