Replace all non digits with an empty character in a string

Question

public static String removeNonDigits(final String str) {
   if (str == null || str.length() == 0) {
       return "";
   }
   return str.replaceAll("/[^0-9]/g", "");
}

This should only get the Digits and return but not doing it as expected! Any suggestions?

Answer 1

Java is not Perl :) Try "[^0-9]+"

Answer 2

Try this:

public static String removeNonDigits(final String str) {
   if (str == null || str.length() == 0) {
       return "";
   }
   return str.replaceAll("\\D+", "");
}

Answer 3

public String replaceNonDigits(final String string) {
    if (string == null || string.length() == 0) {
        return "";
    }
    return string.replaceAll("[^0-9]+", "");
}

This does what you want.

Answer 4

I'd recommend for this particular case just having a small loop over the string

(untested)

StringBuilder sb = new StringBuilder;
for(int i = 0; i < s.length(); i++) {
   char ch = s.charAt(i);
   if (ch =='0' || ch == '1' || ch == '2'....) {
     sb.add(ch);
   }
}
return sb.toString();