英文:
Java Comparator.nullsLast and Comparator.nullsFirst not working as expected
问题
以下是您提供的内容的中文翻译：
我有以下方法，在尝试按列表中为null的字段进行排序时，在sort()中抛出NPE：
private List<MobileSearch> sortAscAndDesc(final MobilesPostResponse mobilesPostResponse,final String[] split,final Comparator<MobileSearch> comparing) {final var direction = getDirection(split);final var modifiableList = new ArrayList<MobileSearch>(mobilesPostResponse.getMobiles());final var comparator = direction.equals(Constants.ASC)? comparing.thenComparing(Comparator.nullsLast(comparing)): comparing.thenComparing(Comparator.nullsFirst(comparing.reversed()));modifiableList.sort(comparator);return modifiableList;}
作为参数传递了一个比较器，该比较器使用了几个keyExtractors。
您可以在下面看到一些方法调用：
final var sortedList = sortAscAndDesc(mobilesPostResponse, split, Comparator.comparing(MobileSearch::getMsisdn));final var sortedList = sortAscAndDesc(mobilesPostResponse, split, Comparator.comparing(MobileSearch::getAssignedProfile));
我想要的只是在每种情况下应用modifiableList.sort()时避免获取NPE，但是使用我的代码片段无法实现。有什么想法？
英文:
I have the following method, which throws NPE in sort() when I am trying to sort by a field which is null in the list :
private List<MobileSearch> sortAscAndDesc(final MobilesPostResponse mobilesPostResponse,final String[] split,final Comparator<MobileSearch> comparing) {final var direction = getDirection(split);final var modifiableList = new ArrayList<MobileSearch>(mobilesPostResponse.getMobiles());final var comparator = direction.equals(Constants.ASC)? comparing.thenComparing(Comparator.nullsLast(comparing)): comparing.thenComparing(Comparator.nullsFirst(comparing.reversed()));modifiableList.sort(comparator);return modifiableList;}
A comparator is passed as a parameter which is using several keyExtractors.
You can see below some method calls :
final var sortedList = sortAscAndDesc(mobilesPostResponse, split, Comparator.comparing(MobileSearch::getMsisdn));final var sortedList = sortAscAndDesc(mobilesPostResponse, split, Comparator.comparing(MobileSearch::getAssignedProfile));
All I want is to avoid getting NPE when applying the modifiableList.sort() in EVERY case, but with my piece of code I can not achieve it. Any ideas?
答案1
得分: 2
您正在使用comparing.thenComparing(...)对空值进行比较，然后才使用Comparators.nulls...(..)。您只需要使用Comparator.nulls...(..)，如下所示：
private List<MobileSearch> sortAscAndDesc(final MobilesPostResponse mobilesPostResponse,final String[] split,final Comparator<MobileSearch> comparing) {final var direction = getDirection(split);final var modifiableList = new ArrayList<MobileSearch>(mobilesPostResponse.getMobiles());final var comparator = direction.equals(Constants.ASC)? Comparator.nullsLast(comparing): Comparator.nullsFirst(comparing.reversed());modifiableList.sort(comparator);return modifiableList;}
英文:
You are using the comparing comparator on the null values by using comparing.thenComparing(...) and then only you use the Comparators.nulls...(..). You just need the Comparator.nulls...(..) like this :
private List<MobileSearch> sortAscAndDesc(final MobilesPostResponse mobilesPostResponse,final String[] split,final Comparator<MobileSearch> comparing) {final var direction = getDirection(split);final var modifiableList = new ArrayList<MobileSearch>(mobilesPostResponse.getMobiles());final var comparator = direction.equals(Constants.ASC)? Comparator.nullsLast(comparing): Comparator.nullsFirst(comparing.reversed());modifiableList.sort(comparator);return modifiableList;}
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