Question

I’m trying to serialize an object and then deserialize it after sending its data to a client program.

Here’s an example of how the object’s inheritance works. The object I’m serializing and deserializing is person.

Living -> Animal -> NPC -> Person -> Child

Living, Animal, and NPC do not implement Serializable. I can not change those three classes. Person and Child do implement Serializable. Person and Living are also abstract classes. I can serialize a Person (who is a Child) just fine and send it, but when I attempt to deserialize a Person (who is a Child), I get an InvalidClassException on Child, saying “no valid constructor”.

Why is this happening? Must Living, Animal, and NPC all implement Serializable?

Answer 1

Good explanation is done in answers for following question
Deserializing an ArrayList. no valid constructor

Long story short – you need no-arg constructor for first nonserializable super class of your class, NPC in your case.

If you don’t have an access to NPC and it doesn’t contain no-arg constructor – then you can add one more ‘fake’ class to hierarchy which will choose the correct one. E.g.

class SomeClass extends NPC {
// will be called during deserialization
public SomeClass(){
// call custom constructor of NPC
super(null);
}
}

class Person extends SomeClass implements Serializable {
// ..
}