Everything's Final

Question

I've been using PMD to help spot potential problems in my Java code, and I've been finding its advice to be split between the useful, the idiosyncratic, and the "WTF?!".

One of the things it keeps telling me to do is to use the final keyword for literally every variable I can attach it to, including input parameters. For actual constants this seems sensible, but for other stuff it just strikes me as odd, possibly even a tad counterproductive.

Are there concrete advantages/disadvantages to hanging final on every variable declaration you possibly can?

Answer 1

This is a common idiom for tools like PMD. For example, below are the corresponding rules in Checkstyle. It's really a matter of style/preference and you could argue for both sides.

In my opinion, using final for method parameters and local variables (when applicable) is good style. The "design for extension" idiom is debatable.

• http://checkstyle.sourceforge.net/config_misc.html#FinalParameters
• http://checkstyle.sourceforge.net/config_design.html#DesignForExtension
• http://checkstyle.sourceforge.net/config_coding.html#FinalLocalVariable

Answer 2

final tells the reader that the value assigned first is the same at any time later. Hence a missing final tells the reader that the value will change later, and to take that into account.

Answer 3

See http://stackoverflow.com/questions/137868/using-final-modifier-whenever-applicable-in-java

Answer 4

PMD also has option rules you can turn on that complains about final; it's an arbitrary rule.

If I'm doing a project where the API is being exported to another team - or to the world - leave the PMD rule as it stands. If you're just developing something that will forever and always be a closed API, disable the rule and save yourself some time.