How can I strip all non digits in a string except the first character?

Question

I have a string that I want to make sure that the format is always a + followed by digits.
The following would work:

String parsed = input         


        

Answer 1

You can use this expression:

String r = s.replaceAll("((?

The idea is to replace any non-digit when it is not the initial character of the string (that's the (? part with a lookbehind) or any character that is not a digit or plus that is the initial character of the string (the ^[^0-9+] part).

Demo.