java - Why declare a function argument to be final? - Stack Overflow

java - Why declare a function argument to be final? - Stack Overflow
There are two main reasons you might want to mark an argument final. First, if you're planning on using the argument in an anonymous inner class, then you must mark it final so that it can be referenced in that class. This is actually a pretty common use case for marking arguments final.
The other common reason to mark arguments final is to prevent yourself from accidentally overwriting them. If you really don't want to change the arguments, then perhaps you should mark them final so that if you actually do, you'll get the error at compile-time rather than finding out at runtime that your code has a bug.

Is there any performance reason to declare method parameters final in Java?
The final keyword does not appear in the class file for local variables and parameters, thus it cannot impact the runtime performance. 
It's only use is to clarify the coders intent that the variable not be changed (which many consider dubious reason for its usage), and dealing with anonymous inner classes.

There is a lot of argument over whether the final modifier on the method itself has any performance gain since the methods will be inlined by the optimizing compiler at runtime anyway, regardless of the modifier. In this case it should also only be used to restrict the overriding of the method.

Use final liberally
The final keyword has more than one meaning:
a final class cannot be extended
a final method cannot be overridden
final fields, parameters, and local variables cannot change their value once set

Using final:
clearly communicates your intent
allows the compiler and virtual machine to perform minor optimizations
clearly flags items which are simpler in behaviour - final says, "If you are looking for complexity, you won't find it here."

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