What is an invariant?

Question

The word seems to get used in a number of contexts. The best I can figure is that they mean a variable that can't change. Isn't that what constants/finals are for?

Answer 1

Invariant is generally used in the context of loops and you will hear the term "loop invariant". Loop invariant means its value is not going to change inside the loop so its more efficient to do its computation/calculation once before entering the loop.