Is there a regex to mask all characters excluding first & last characters in each word

Question

For example, I have below list of words to be masked.

India
Australia
North America
South America
White House building

I need an output like below.

Ixxxa
Axxxxxxxa
Nxxxh Axxxxxa
Sxxxh Axxxxxa
Wxxxe Hxxxe bxxxxxxg

using below expression I'm able to mask last characters including spaces.

return input.replaceAll("[\\s()]+", " ").replaceAll("\\d(?=(?:\\D*\\d){4})","X");

Answer 1

To match a non whitepace char except for the "outer" ones, you can assert a non whitespace char \S to the left and to the right right:

(?<=\S)\S(?=\S)

In Java

(?<=\\S)\S(?=\\S)

See a regex demo and a Java demo.

Java example:

    String regex = "(?<=\\S)\\S(?=\\S)";
    String string = "India\n"
 + "Australia\n"
 + "North America\n"
 + "South America\n"
 + "White House building\n"
 + "a\n"
 + "ab\n"
 + "abc\n"
 + "tthis123_isatest\n"
 + "!@#$%";

    String result = string.replaceAll(regex, "x");
    System.out.println(result);

Output

Ixxxa
Axxxxxxxa
Nxxxh Axxxxxa
Sxxxh Axxxxxa
Wxxxe Hxxxe bxxxxxxg
a
ab
axc
txxxxxxxxxxxxxxt
!xxx%