java class that filter numbers out of a string

public class Numerize {
    final static private String allnums = "0123456789";
    public  static  String filter(String s1){
        char[] arr = s1.toCharArray();
        String result="";
        for (char ot:arr) {
            if(allnums.contains(ot + "")){result+= ot;}
        }
        return result;
    }
}