So having to write extra code to extend your versioning system to parse whatever language your code is in and then check it to see if you've altered a variable

So having to write extra code to extend your versioning system to parse whatever language your code is in and then check it to see if you've altered a variable value doesn't increase bloat, but adding the 'final' keyword does? There are other problems with that idea, the first of which is that if someone else takes your code and extends it (say, for an open source project) they won't have the same "checking system" that you have, and so it won't catch their mistakes (while using "final" would). Also, I'm not a Java programmer (I mostly use C# or C), but marking classes/methods/variables in C# as 'sealed', 'final', 'static', etc. actually increases the running speed of that program on the CLR because it is able to skip some safety checks on the IL code when it is executed; I don't know that the JVM does that, but it might be worth looking into.