Question

I have an interface Serializable. This class have methods for each Item subclass in my application. However not all classes that implements Serializable have a reasonable implementation of the serialize method. Some of the serializers should not be able to serialize all the different objects because of security constraints in my application.

How should I solve this? Should I serialize a message that says “Serializer can’t serialize object because of security constraints.” or should I throw an RuntimeException? Or are there other ways of “fixing” this?

Answer 1

You would violate one important principle with your logic: Interface Segregation Principle

The Interface Segregation Principle states that clients should not be
forced to implement interfaces they don’t use. Instead of one fat
interface many small interfaces are preferred based on groups of
methods, each one serving one submodule.

So, I would create two distinct base classes to achieve your requirement:

• Item
• SerializableItem

And your visitor would only rely on SerializableItem objects:

public void visit(SerializableItem sItem) 

Of course, it is possible to gather only common behaviour (unrelated to serialization so) of both classes within a kind of AbstractItem, as long as the visitor doesn’t deal with it.