The instantiation mode can be configured globally or on a per class basis.
Java:Db4o.configure().callConstructors(true)
This will configure db4o to use constructors to reinstantiate any object from the database. (The default is false).
Java: Db4o.configure().objectClass(Foo.class).callConstructor(true)
This will configure db4o to use constructor calls for this class and all its subclasses.