What does it mean to have a final input parameter in method signature?

Question

What would be the reason for doing the below:

public void processSomething(final String hello, final String two, final Car car){}

as opposed to:

public void processSomething(String hello, String two, Car car){}

Answer 1

It means that within the method, you can't assign new values to the parameters.

A common reason for wanting to do this is to be able to use the parameters within anonymous inner classes which can only reference final local variables, including parameters.

Another reason for doing this is if your coding style favours declaring all local variables as final if possible. (Personally I try to treat them as final, but avoid actually declaring them that way, as it adds cruft.)

Answer 2

It means you cannot change the references. String is immutable, but if Car is mutable you can change the fields in that Car, you can't change it to another Car.