java如何为集合正确编写此比较器。排序（arrayList、comparator）？

Question

我写了一个比较器来比较两个物体

希望每个对象的方法都是不言自明的。当我将我的ArrayList放入Collections.sort(arrayList, comparator)时，它根本不会排序

public int compare(User o1, User o2) {
final int followersComparison = Integer.compare(o2.getWhoThisUserIsBeingFollowedBy().size(), o1.getWhoThisUserIsBeingFollowedBy().size());

if (followersComparison != 0) {
  return followersComparison;
}

final int followingComparison = Integer.compare(o2.getWhoThisUserIsFollowing().size(), o1.getWhoThisUserIsFollowing().size());

if (followingComparison != 0) {
  return followingComparison;
}

// Note here o1 and o2 is in opposite order than above
return  Integer.compare(o1.getUserId(), o2.getUserId());

}

我希望Collections.sort能根据这个比较器对我的ArrayList进行排序，但它没有

Answer 1

这是怎么回事：

public int compare(User o1, User o2) {
    final int followersComparison = Integer.compare(o2.getWhoThisUserIsBeingFollowedBy().size(), o1.getWhoThisUserIsBeingFollowedBy().size());

    if (followersComparison != 0) {
      return followersComparison;
    }

    final int followingComparison = Integer.compare(o2.getWhoThisUserIsFollowing().size(), o1.getWhoThisUserIsFollowing().size());

    if (followingComparison != 0) {
      return followingComparison;
    }

    // Note here o1 and o2 is in opposite order than above
    return  Integer.compare(o1.getUserId(), o2.getUserId());

  }

似乎在比较数字时，您可能遗漏了其他一些部分（例如，如果o1.getwhoThisUserIsBeingFollowedBy().size() > 02.getwhoThisUserIsBeingFollowedBy().size()只返回1，但如果是相反的情况，该怎么办）。我倾向于犯同样的错误，这就是为什么我更喜欢使用整数。比较