Recursive problem

public class RunningClass {

    public static void main(String [] args)
    {
        List<String> list = new LinkedList<>();
        process(Collections.singletonList("2890"), list);

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

    public static void process(List<String> parts, List<String> list) {

        for (int partIndex = 0; partIndex < parts.size(); partIndex++) {

            String part = parts.get(partIndex);

            List<String> previousPart = partIndex > 0? parts.subList(0, partIndex) : null;
            List<String> lastParts = partIndex < parts.size() - 1? parts.subList(partIndex + 1, parts.size()) : null;

            for (int i = 1; i < part.length(); i++) {

                List newParts = new LinkedList();
                if (previousPart != null) newParts.addAll(previousPart);

                newParts.add(part.substring(0, i));
                newParts.add(part.substring(i));

                if (lastParts != null) newParts.addAll(lastParts);

                process(newParts, list);
            }

        }

        String result = "";
        for (String part : parts) {
            result = result + part + " ";
        }
        result = result.trim();

        if (!list.contains(result)) {
            list.add(result);
        }

    }

}