Implementing versioning with a Java SDK

Question

I have an SDK that I supply to vendors who want to develop custom classes that extend the classes in my SDK .jar (the specifics of the SDK is unimportant). I am trying to devise a way find out what version of the SDK the vendor compiled their class against without requiring the vendor to make code changes.
In my first attempt, I included a final method in the SDK called getVersion() that returned "1.0". The problem with this approach is that when I instantiate the vendor's class (that extended the class in the SDK), and call getVersion() on the vendor's class, I get the value "1.0" from the base class, not the vendor class. Therefore, if the vendor compiles his .class file with the "1.0" version of the SDK, and I later upgrade my SDK to "2.0", whenever I call getVersion() from the vendor's .class file, I always get the version from the base class (i.e. "2.0") and not the version that they used originally ("1.0").
What I am trying to do is figure out a way to mark a vendor's class in a manner that is independent of the SDK. Obviously, I could tell the vendor to implement getVersion() and return the number that the SDK is at, or I could have the vendor implement another class called "SDKVersion" and change this to "SDKVersion2_0"..."SDKVersion3_0" as needed, but these require the vendor to take specific action to identify what version they compiled against. I would rather the vendor be unaware of the versioning if possible.
Is there some way to "mark" the class when it is compiled with a number or name? That's all I need to do to accomplish my versioning goals.
Thanks for any help you have,
Michael

Answer 1

You mean, some option of the javac command that would automatically add a getVersion() method to your code? Or a constant containing the version number? When you put it that way, the answer is obviously NO. If you want to require your vendors to implement getVersion(), then declare your class as abstract and define an abstract getVersion() method.