How can I serialize an interface?

Question

Suppose I have a Serializable class ShapeHolder that owns an object that implements a Serializable Shape interface. I wa

Answer 1

I want to make sure the correct concrete shape object is saved (and the correct type is later restored).

Java's default serialization (ObjectInputStream & ObjectOutputStream) does that out-of-the-box. When serializing, Java writes there the name of the concrete class and then uses in when deserializing.