a natural sort implementation using ruby

natural_sort.rb

def first_number_occurrence_for(string)
    string.match(/(\d+)/).captures.first.to_i
end

def natural_sort(items)
      items.sort { |a, b| first_number_occurrence_for(a) <=> first_number_occurrence_for(b) }
end

natural_sort ["z123.txt", "z1.txt", "z100.txt", "z200.txt", "z3.txt"]

NaturalSort.java

public class NaturalSort {

        public static Integer firstNumberOccurrenceFor(String string) {
                java.util.regex.Matcher matcher = java.util.regex.Pattern.compile("^\\D*(\\d+).*").matcher(string);
                matcher.find();
                return Integer.valueOf(matcher.group(1));
        }

        public static java.util.List<String> naturalSort(java.util.List<String> items) {
                java.util.List<String> sortedItems = new java.util.ArrayList<String>(items);
                java.util.Collections.sort(sortedItems, new java.util.Comparator<String>() {
                        public int compare(String a, String b) {
                                return firstNumberOccurrenceFor(a).compareTo(firstNumberOccurrenceFor(b));
                        }
                });
                return sortedItems;
        }

        public static void main(String[] args) {
                System.out.println(naturalSort(java.util.Arrays.asList("z123.txt", "z1.txt", "z100.txt", "z200.txt", "z3.txt")));
        }
}