Regex for phone number masking in Java

Question

I need to mask a phone number

90 511 619 11 21

like this

5**6**1*2*

first I'm checking if it contains 90 (country code) and removing it

if (number.length() > 2 && number.substring(0,2).contains("90")){
            number = number.replaceAll(number.substring(0,2), "");
        }

then I'm removing all the spaces but I'm stuck at the regex part.

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

Answer 1

We can solve this problem without using any capture groups:

String input = "533 619 11 21";
input = input.replaceAll("(?<=\\d)\\d", "*").replaceAll(" ", "");
System.out.println(input);

5**6**1*2*

The replacement logic here is that any single digit which is immediately preceded by a digit gets replaced with asterisk. This of course spares the first digit.

Note that I assume that you already have some means to remove the country code.

Demo

Answer 2

\d(?<=\d{2})

Regex101 Demo

For your code, replace the space after *:

number = number.replaceAll("\\d(?<=\\d{2})", "*").replaceAll(" ", "");