Java: versioned data structures?

Question

I have a data structure that is pretty simple (basically a structure containing some arrays and single values), but I need to record the history of the data structure so that I

Answer 1

Either do as you already suggested, or have a base class of some sort with subclasses that represent the different changes. Then get the proper class at run-time by passing the version/timestamp/whatever to a factory that hands you back the right one.