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javajava-streamcollectors

will objectList.stream().collect(Collectors.toMap(Object::getField, Function.identity)) return null?

i've got a list form DB, then i use the function above to translate it to a hashMap(already check out this list is not null or emptiy). but the sonarLint keeps telling me that the function above might return null, and it might caught NPE. And when i use enhanced for loop, the warning will disappear.

i can't find out why eventualy, hope you help me out of here. Thanks a lot.

the code below that sonarLint says might return null:

return objectList.stream().filter(Objects::nonNull).collect(Collectors.toMap(Object::getField, Function.identity()));

the code below that sonarLint says it's ok:

   Map<String, Object> map = new HashMap<>();
   for(Object obj : ObjectList) {
       map.put(obj.getField(), obj);
   }
   return map;
Solution

  • No, it won't. The whole collection framework is build in ways to ensure that you don't end up with null where some empty collection could be provided instead.

    So: the collector will not return null.

    But: depending on your context, obj.getField() might return null. And there are conditions where collection methods throw NPEs for null keys.