Java Sort List of Lists

Question

How would I sort a list of lists in Java in lexicographical order using Collections.sort() or another sorting method?

private List>         


        

Answer 1

Improved MartinS answer using Java 8 stream API

possiblePoles = possiblePoles.stream().sorted((o1,o2) -> {
             for (int i = 0; i < Math.min(o1.size(), o2.size()); i++) {
                  int c = o1.get(i).compareTo(o2.get(i));
                  if (c != 0) {
                    return c;
                  }
                }
                return Integer.compare(o1.size(), o2.size());
         }).collect(Collectors.toList());

Answer 2

You will have to implement your own Comparator class and pass in an instance to Collections.sort()

class ListComparator<T extends Comparable<T>> implements Comparator<List<T>> {

  @Override
  public int compare(List<T> o1, List<T> o2) {
    for (int i = 0; i < Math.min(o1.size(), o2.size()); i++) {
      int c = o1.get(i).compareTo(o2.get(i));
      if (c != 0) {
        return c;
      }
    }
    return Integer.compare(o1.size(), o2.size());
  }

}

Then sorting is easy

List<List<Integer>> listOfLists = ...;

Collections.sort(listOfLists, new ListComparator<>());