Here's a more verbose solution. Less elegant, but probably faster:
public static String stripNonDigits(final String input){
final StringBuilder sb = new StringBuilder();
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();
}
Test Code:
public static void main(final String[] args){
final String input = "0-123-abc-456-xyz-789";
final String result = stripNonDigits(input);
System.out.println(result);
}
Output:
0123456789
BTW: I did not use Character.isDigit(ch) because it accepts many other chars except 0 - 9.