Scala: How to mask the first N characters of a string

Question

Given a string that represents a credit card number...

val creditCardNo = "1111222233334444"

... how do I mask the first 12 characters with *?

val maskedCreditCardNo = "************4444"

Answer 1

Just use drop or substring on the original number, and prepend the right number of "*":

"*" * 12 + (creditCardNo drop 12)

Answer 2

Replace all digit symbols unless 4 characters remain:

creditCardNo.replaceAll("\\d(?=\\d{4})", "*")