[regex] Regular expression to match exact number of characters?

I need a regular expression that will match any three uppercase letters, so AAA or ABC or DKE. It can't match four or more though, like AAAA or ABCDEF or aBBB.

My solution: ^([A-Z][A-Z][A-Z])$

Questions:

1. Is this correct?
2. Is there another way, just for the sake of learning?