Pure Danger Tech


A final bit of advice

26 Nov 2008

Or maybe that should be “a bit of final advice”. :) There was a question on StackOverflow about best practices around using final in parameters, local variables, fields, etc and my answer seems to have been popular. I’ll repeat it here merely to make it easier for me to find later.

Obsess over:

  • Final fields – Marking fields as final forces them to be set by end of construction, making that field reference immutable. This allows safe publication of fields and can avoid the need for synchronization on later reads. (Note that for an object reference, only the field reference is immutable – things that object reference refers to can still change and that affects the immutability.)
  • Final static fields – Although I use enums now for many of the cases where I used to use static final fields.

Consider but use judiciously:

  • Final classes – Framework/API design is the only case where I consider it.
  • Final methods – Basically same as final classes. If you’re using template method patterns like crazy and marking stuff final, you’re probably relying too much on inheritance and not enough on delegation.

Ignore unless feeling anal:

  • Method parameters and local variables – I RARELY do this largely because I’m lazy and I find it clutters the code. I will fully admit that marking parameters and local variables that I’m not going to modify is “righter”. I wish it was the default. But it isn’t and I find the code more difficult to understand with finals all over. If I’m in someone else’s code, I’m not going to pull them out but if I’m writing new code I won’t put them in. One exception is the case where you have to mark something final so you can access it from within an anonymous inner class.