[java] Extract digits from a string in Java

A:
str.replaceAll("[^0-9]", "")

B:
str.replaceAll("\\D+","")

C:
public static String stripNonDigits(
  final CharSequence input /* inspired by seh's comment */){
  final StringBuilder sb = new StringBuilder(
  input.length() /* also inspired by seh's comment */);
  for(int i = 0; i < input.length(); i++){
  final char c = input.charAt(i);
  if(c > 47 && c < 58){
  sb.append(c);
  }
  }
  return sb.toString();}

http://stackoverflow.com/questions/4030928/extract-digits-from-a-string-in-java