如何在不区分大小写的情况下按字母顺序对ArrayList进行排序，并在末尾使用任意数字字符串

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class ArrayListSortExample {
    public static void main(String[] args) {
        ArrayList<String> list = new ArrayList<>();
        list.add("abc");
        list.add("def");
        list.add("123");
        list.add("xyz");
        list.add("456");

        Collections.sort(list, new IgnoreCaseComparator());

        for (String str : list) {
            System.out.println(str);
        }
    }

    static class IgnoreCaseComparator implements Comparator<String> {
        @Override
        public int compare(String s1, String s2) {
            String pattern = "([a-zA-Z]+)(\\d+)?";
            Pattern p = Pattern.compile(pattern);
            Matcher m1 = p.matcher(s1);
            Matcher m2 = p.matcher(s2);

            if (m1.find() && m2.find()) {
                String letters1 = m1.group(1);
                String letters2 = m2.group(1);
                int result = letters1.compareToIgnoreCase(letters2);

                if (result == 0) {
                    String digits1 = m1.group(2);
                    String digits2 = m2.group(2);

                    if (digits1 != null && digits2 != null) {
                        return Integer.compare(Integer.parseInt(digits1), Integer.parseInt(digits2));
                    } else if (digits1 != null) {
                        return -1;
                    } else if (digits2 != null) {
                        return 1;
                    }
                }

                return result;
            }

            return 0;
        }
    }
}

abc
def
xyz
123
456