In an OO language (e.g. but not limited to Java) how do you fix duplicate code depending on the scope of it's occurrence? I would start with (for example)
Recently I found a good answer to my question in Uncle Bob's "Clean Code", which I want to share. He differentiates three types of duplication
Pieces of identical code should be replaced with a single method. So the fix would be to extract the method and delegate to common behaviour.
SthUtil or SthLib).cases of switch/case and if/else that always test for the same set of conditions.
Modules that implement similar algorithms. These are hardest to find, as no clone detector can find them.
Also a valid point mentioned by Oded, when dealing with different versions of libraries
In the end the best one sentence to answer my question is by stimms:
code reuse method used in OO languages is objects.
In general - consolidate duplicate code into a single place and ensure original duplication site is calling the consolidated place.
In your examples, within a class this would be the extracted method and within a set of classes the pulled-up method within the base class.
In copy-paste code, this would be to remove the duplicates and ensuring that any users now use the single copy (in whatever level this is).
When dealing with different versions of libraries, consolidate on a single version (if possible).
I guess this is an open ended question but it also depends on the state of the code as well. I mean you can tolerate the duplicate code a little bit depending on the context. Rule of three is good for this matter.
Rule Of Three The first time you do something, you just do it. The second time you do something similar, you wince at the duplication, but you do the duplicate thing anyway. The third time you do something similar, you refactor.
Although this is pretty much arguable, this post also considers cases where you would tolerate duplicate code.
