Type cast not working using map function in Java 8

Question

I am comparing two lists.

List allUserGroups = UserBC.getAllGroupsForUser(userId, deptID);
List<String> confUserGroups= Arrays.asList(configuredSet);

List one returns Object which I need to typecast to GroupData entity. GroupData has multiple fields and want to compare for one of the fields 'id'. So I used map function to typecast as below,

isValuePresent = allUserGroups.stream().map(p -> (GroupData) p).anyMatch(p -> confUserGroups.contains(p.getId()));

Issue is, for p.getId() its again asking for typecast. Compiler asks to add cast again. Can anyone please suggest if I missed anything.

EDIT1: id is of long type otherwise I could have used ((GroupData)p).getId()

EDIT2: Modified the code as answered by Joop, but getting same error

You should be able to skip the `map` part. Simply do the cast on `((GroupData)p).getId()` — jensgram, Jul 21 '17 at 11:04
@jensgram I have edited my question. The problem here is 'id' is of long type and i again need to convert it to String for caomparing. Thats why I was typecasting — Vikas, Jul 21 '17 at 11:12
@VikasYadav you are missing one additional cast `.map(GroupData::getId).anyMatch(configuredVipUsetGroups::contains)` — Anton Balaniuc, Jul 21 '17 at 13:28
@AntonBalaniuc I have tried that also, `isValuePresent = allUserGroups.stream() .map(GroupData.class::cast) .map(GroupData::getId) .anyMatch(confUserGroups::contains);` But here getting,'The type GroupData does not define getId(Object) that is applicable here' as getId is not having any argument. — Vikas, Jul 21 '17 at 13:41
`List` without a type argument is a raw type. Don't use raw types, unless you absolutely have to (because you are dealing with a very old API that doesn't use generics). See: [What is a raw type and why shouldn't we use it?](https://stackoverflow.com/questions/2770321/what-is-a-raw-type-and-why-shouldnt-we-use-it) — Jesper, Jul 27 '17 at 07:53
@Jesper You are correct but This one is already implemented in our application. So I don't have an option to use generic list. So need to do type cast it. — Vikas, Jul 27 '17 at 07:56
The type of `p` is `Object`, so each time you need to call a method on it from another type, you need to cast it first. — Jesper, Jul 27 '17 at 07:57
@Jesper Please check my answer. I know if I explicitly typecast, it will work. Issue is its not working using map method to typecast — Vikas, Jul 27 '17 at 08:01

Anton Balaniuc · Accepted Answer · 2017-07-21T14:56:16.383

You might try to use something like this:

allUserGroups.stream()
    .map(GroupData.class::cast)
    .map(GroupData::getID)
    .anyMatch(confUserGroups.contains)

for example with String class:

List<Object> list = Arrays.asList("a","ab","abc");
list.stream()
        .map(String.class::cast) // cast to String
        .map(String::getBytes) // call getBytes on every element
        .forEach(System.out::println);

score 1 · Answer 2 · answered Jul 21 '17 at 11:31

1

Both p's are different variables.

isValuePresent = allUserGroups.stream()
    .map(GroupData.class::cast)
    .anyMatch(p -> confUserGroups.contains(p.getId()));

isValuePresent = allUserGroups.stream()
    .map(GroupData.class::cast)
    .map(GroupData::getId)
    .anyMatch(confUserGroups::contains);

answered Jul 21 '17 at 11:31

Joop Eggen

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7
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First part of your answer is throwing same error i. e add cast to p. For second part, getting 'The type GroupData does not define getId(Object) that is applicable here'. getId is not having any argument. – Vikas Jul 21 '17 at 11:50

cjangaritas · Answer 3 · 2020-04-17T13:56:14.657

1

If you already know the type of the values on the list, you could cast the list and then use the stream.

List<GroupData> allUserGroups = (List<GroupData>)UserBC.getAllGroupsForUser(userId, deptID);
confUserGroups= Arrays.asList(configuredSet);

isValuePresent = allUserGroups.stream().anyMatch(p -> confUserGroups.contains(p.getId()));

edited Apr 17 '20 at 13:56

answered Mar 18 '19 at 23:31

cjangaritas

64
5

Vikas · Answer 4 · 2017-07-21T11:29:40.467

0

Adding String.valueOf and directly typecasting id solved my issue.

isValuePresent = allUserGroups.stream().anyMatch(p -> configuredVipUserGroups.contains(String.valueOf(((GroupData) p).getId())));

But I still wonder why .map(p -> (GroupData) p) was not able to typecast.

edited Jul 21 '17 at 11:29

answered Jul 21 '17 at 11:22

Vikas

6,868
4
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score 0 · Answer 5 · edited Jul 21 '17 at 12:31

0

Use casting in contains function no need to cast before it.

isValuePresent = allUserGroups.stream()
                            .map(p -> p)
                            .anyMatch(p -> confUserGroups.contains( (GroupData)p.getId()));

edited Jul 21 '17 at 12:31

azro

53,056
7
34
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answered Jul 21 '17 at 11:53

poonam

49
1
4

check edit1, id is of long type otherwise I could have used ((GroupData)p).getId() – Vikas Jul 21 '17 at 11:58

Type cast not working using map function in Java 8

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