How to replace all characters in a user input stri

问题:

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 to guess it one letter at a time. Between guesses, the phrase must be displayed as all question marks except the letters that were guessed correctly. Our class has only really covered some very basic methods, if-else statements and loops up to this point, but I'm trying to research some string methods that may make this a bit easier.

I know of the replace(), replaceAll() and contains() methods, but was wondering if there is a method which allows you to replace all but one character of your choice in a string.

Thanks in advance

回答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.