Activity A / B - Where To Declare Keys Of Bundles

I have a little doubt, I spend data from Activity A to B with a bundle in the intent.Where I should declare the keys? In Activity A or B? Only to avoid confusion, I'm talking about the string that defines the data that will be set in the Bundle.Ex: public static final String KEY = "MyKey";

I declare always in the Activity A, but I think that if I could let all the keys in a file would be better, like keys.java or something like that.Obviously, this is nothing that is generating errors, just a doubt about convention, a thing that I consider very important in software development.