This looks like a job for regular expressions
!
String s = "sdf234sdf234";
System.out.println(s.replaceAll("\\D", "").length());
Or perhaps your after each multiple digit number instance?
String s = "sdf234sdf234sdf23";
s = s.replaceAll("^\\D+|\\D+$", "").replaceAll("\\D+", ",");
List<String> numbers = Arrays.asList(s.split(","));
System.out.println(numbers);