# Type mismatch: inferred type is kotlin.collections.ArrayList\<WorkerUser\> /\* = java.util.ArrayList\<WorkerUser\> but kotlin.collections.ArrayList\<RecyclerViewAdapter.ListItem\> java.util.ArrayList\<RecyclerViewAdapter.ListItem\> was expected

**URL:** https://discuss.kotlinlang.org/t/type-mismatch-inferred-type-is-kotlin-collections-arraylist-workeruser-java-util-arraylist-workeruser-but-kotlin-collections-arraylist-recyclerviewadapter-listitem-java-util-arraylist-recyclerviewadapter-listitem-was-expected/10558
**Category:** Support
**Created:** [November 28, 2018, 2:32pm UTC](https://discuss.kotlinlang.org/t/type-mismatch-inferred-type-is-kotlin-collections-arraylist-workeruser-java-util-arraylist-workeruser-but-kotlin-collections-arraylist-recyclerviewadapter-listitem-java-util-arraylist-recyclerviewadapter-listitem-was-expected/10558 "2018-11-28T14:32:01Z")
**Posts on this page:** 2
**Page:** 1

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### Author: ![Damirme](https://avatars.discourse-cdn.com/v4/letter/d/d9b06d/32.png) [@Damirme](https://discuss.kotlinlang.org/u/Damirme)
#### Post date: [November 28, 2018, 2:32pm UTC](https://discuss.kotlinlang.org/t/type-mismatch-inferred-type-is-kotlin-collections-arraylist-workeruser-java-util-arraylist-workeruser-but-kotlin-collections-arraylist-recyclerviewadapter-listitem-java-util-arraylist-recyclerviewadapter-listitem-was-expected/10558/1 "2018-11-28T14:32:01Z")

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Type mismatch: inferred type is kotlin.collections.ArrayList /\* = java.util.ArrayList _/ but kotlin.collections.ArrayList\<RecyclerViewAdapter.ListItem\> /_ = java.util.ArrayList\<RecyclerViewAdapter.ListItem\> \*/ was expected

my WorkerUser class is implementing RecyclerViewAdapter.ListItem interface

in Java it works, but why this is not working here?

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### Author: ![pdvrieze](https://sea1.discourse-cdn.com/flex019/user_avatar/discuss.kotlinlang.org/pdvrieze/32/1882_2.png) [@pdvrieze](https://discuss.kotlinlang.org/u/pdvrieze)
#### Post date: [November 28, 2018, 9:10pm UTC](https://discuss.kotlinlang.org/t/type-mismatch-inferred-type-is-kotlin-collections-arraylist-workeruser-java-util-arraylist-workeruser-but-kotlin-collections-arraylist-recyclerviewadapter-listitem-java-util-arraylist-recyclerviewadapter-listitem-was-expected/10558/2 "2018-11-28T21:10:14Z")

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You have a covariance issue. A list of WorkerUser is not a valid list of ListItem as it is possible to take a list of ListItem, add an element that is a ListItem but not WorkerUser. You probably wanted to use the readOnly List interface which does not have this issue on the receiver.