Java 8 stream and set attribute from call Boolean method

Question

Please can you help me resolve this issue I am having when attempting to stream through an array list and call a setter based on a method which returns a Boolean.

Written as a for loop, it would look like this:-

for (final PersonDto person : personList) {
    person.setUserCanEdit(userHasWriteRole(person));
}

private Boolean userHasWriteRole(final PersonDto person) {
        return getUserRoles().contains(getReadRole());
    }

I have tried a few variations with no success, along the following lines

final List<PersonDto> results = personList.stream().filter(a -> a.setUserCanEdit(this::userHasWriteRole)).collect(Collectors.toList());

... But it complains with The target type of this expression must be a functional interface

please make clear this private Boolean userHasWriteRole(final PersonDto person) { return getUserRoles().contains(getReadRole()); } — Hadi
– Hadi, Commented Jun 8, 2020 at 10:41
The method isn't really relevant, it has more logic within it, but for the purposes for this issue I wanted to show that it returns a Boolean value. — R111
– R111, Commented Jun 8, 2020 at 10:47

Gavin · Accepted Answer · 2020-06-08 12:14:00Z

1

I think I would go for:

personList.stream()
   .filter(p -> userHasWriteRole(p))
   .forEach(p -> p.setUserCanEdit(true));

I think this keeps the intent clear,

answered Jun 8, 2020 at 12:14

Gavin

1,7771 gold badge21 silver badges37 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Ryuzaki L · Accepted Answer · 2020-06-08 10:35:41Z

0

Since you are updating the objects in array list, you can use forEach

personList.forEach(person ->person.setUserCanEdit(userHasWriteRole(person)));

answered Jun 8, 2020 at 10:35

Ryuzaki L

40.4k14 gold badges81 silver badges111 bronze badges

6 Comments

R111 Over a year ago

I tried this but I get "Type mismatch: cannot convert from void to List<PersonDto>"

Ryuzaki L Over a year ago

forEach method is void type @R111

R111 Over a year ago

so how do I accomplish the desired outcome?

Ryuzaki L Over a year ago

personList will have the desired output, print the list and check it @R111

R111 Over a year ago

Thanks @Deadpool. It looks like that works, but can you tell me why I cant assign the output to a new arraylist? e.g.List<PersonDto> newList = personList.forEach(person ->person.setUserCanEdit(userHasWriteRole(person)));

|

Eklavya · Accepted Answer · 2020-06-08 11:05:41Z

0

The filter() method is an intermediate operation of the Stream interface that allows us to filter elements of a stream that match a given Predicate. You can't update data in the filter. Use forEach for this.

personList.stream().forEach(a -> a.setUserCanEdit(userHasWriteRole(a)));

And if you want to get in new arraylist make a copy of list and do this operations on new list

List<PersonDto> copy = new ArrayList<>(personList);
copy.stream().forEach(a -> a.setUserCanEdit(userHasWriteRole(a)));

edited Jun 8, 2020 at 11:05

answered Jun 8, 2020 at 10:41

Eklavya

18.6k4 gold badges33 silver badges62 bronze badges

Comments

lczapski · Accepted Answer · 2020-06-08 14:00:30Z

0

If you want to have a list with filtered elements and do the setUserCanEdit on every elements in that list; you can do like this:

List<PersonDto> newList = personList.stream()
  .filter(p -> userHasWriteRole(p))
  .collect(Collectors.toList());

newList.forEach(p -> p.setUserCanEdit(true));

answered Jun 8, 2020 at 14:00

lczapski

4,1603 gold badges18 silver badges35 bronze badges

Collectives™ on Stack Overflow

Java 8 stream and set attribute from call Boolean method

4 Answers 4

Comments

6 Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

Comments

6 Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related