How to replace all characters in a user input string except one

Question

I\'m currently in an introductory level Java class, and am working on the classic phrase guess assignment. The object is for one user to enter a secret phrase, and another t

Answer 1

The easiest way is probably to use String.replaceAll():

String out = str.replaceAll("[^a]", "?");

This will leave all letters a intact and will replace all other characters with question marks.

This can be easily extended to multiple characters, like so:

String out = str.replaceAll("[^aeo]", "?");

This will keep all letters a, e and o and will replace everything else.