Java排序列表

Question

如何使用Collections.sort()或其他排序方法按字典顺序对Java列表进行排序？

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

Answer 1

您将必须实现自己的Comparator类并将实例传递给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());
  }

}

然后排序很容易

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

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

Answer 2

使用 Java 8 流 API 改进 MartinS 答案

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());