# A HashMap is not a Map?

**URL:** <https://discuss.kotlinlang.org/t/a-hashmap-is-not-a-map/504>\
**Category:** Uncategorized\
**Created:** [August 23, 2014, 4:08pm UTC](https://discuss.kotlinlang.org/t/a-hashmap-is-not-a-map/504 "2014-08-23T16:08:13Z")\
**Posts on this page:** 1\
**Showing post:** 4

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**Author:** ![abreslav](https://sea1.discourse-cdn.com/flex019/user_avatar/discuss.kotlinlang.org/abreslav/32/8279_2.png) [@abreslav](https://discuss.kotlinlang.org/u/abreslav)\
**Post date:** [August 23, 2014, 10:31pm UTC](https://discuss.kotlinlang.org/t/a-hashmap-is-not-a-map/504/4 "2014-08-23T22:31:14Z")

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Some explanation is available here: [http://blog.jetbrains.com/kotlin/2012/09/kotlin-m3-is-out/](http://blog.jetbrains.com/kotlin/2012/09/kotlin-m3-is-out/)

In short, Java’s Map is mutable, and in Kotlin we replace it with a pair of interfaces (read-only) Map and MutableMap to facilitate better type safety. If these extended Java’s Map, they’d have to be mutable as well.

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