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<List<Integer>> possiblePoles = setPoles();    
System.out.println(possiblePoles)
[[1, 3, 5], [1, 2, 3]]

Answer 1

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<>());