final variable interpretation

Question

I know how the compiler interprets the final keyword in Java, but how should us programmers interpret its meaning? Should it be:

1) This variable cannot be changed (used by inner class for example)

or

2) I'm not planning to change this variable (might have some optimisation benefits for member variables).

I'm asking because I've worked on code where everything is declared final by default (option 2 above) which, in my opinion, devalues the keyword and hides the values that really can't change! Is there still performance benefits in declaring variables final?

Answer 1

Everything being final by default is a good thing. The more you can model your code on immutability, the easier it tends to be to reason about.

Using final is hardly ever about performance in my opinion. It's about making assertions about the rest of the code (nothing changes this variable) which can help a reader to understand the code, and can be checked by the compiler.

EDIT: The above is my view for fields. For local variables (including parameters) I personally only use final when the variable will be used in an anonymous inner class. This is different from fields because:

• It's easy to see the whole context of the method - and if it's not, that's a problem in itself.
• As it doesn't represent the state of an object (or class) the benefits of immutability don't really apply.