# Override class parameter type

**URL:** <https://discuss.kotlinlang.org/t/override-class-parameter-type/17960>\
**Category:** Support\
**Created:** [June 4, 2020, 12:18pm UTC](https://discuss.kotlinlang.org/t/override-class-parameter-type/17960 "2020-06-04T12:18:22Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![Oleg](https://sea1.discourse-cdn.com/flex019/user_avatar/discuss.kotlinlang.org/oleg/32/7609_2.png) [@Oleg](https://discuss.kotlinlang.org/u/Oleg)\
**Post date:** [June 4, 2020, 12:18pm UTC](https://discuss.kotlinlang.org/t/override-class-parameter-type/17960/1 "2020-06-04T12:18:22Z")

</div>

Hi guys,  
I’m new Kotlin and need your help / advice

I have json api where response will always be

> {  
> “code”: 0 // Always integer  
> “error”: {  
> “message”: null, // Either null or string,  
> “context”: // Empty list  
> },  
> “result”: null, // Can be anything, null, string, list  
> }

and I created two generic classes for this

> open class ResponseError(  
> val message: String?,  
> val context: List\<\*\>  
> )
> 
> open class Response(  
> val code: Int,  
> val error: ResponseError,  
> var result: Any?  
> )

now what I want is to override Response for login api call, where “result” will be string

> class TokenResponse(  
> code: Int,  
> error: ResponseError,  
> result: String?  
> ): Response(code, error, result)

but when I access result it’s still showing “Any?” in android studio, shouldn’t it be String? (because I made it more strict with String type)

> Type mismatch.  
> Required: String?  
> Found: Any?

Can’t I change class parameters type hints?

---

<div class="post-metadata">

**Author:** ![Wasabi375](https://sea1.discourse-cdn.com/flex019/user_avatar/discuss.kotlinlang.org/wasabi375/32/4741_2.png) [@Wasabi375](https://discuss.kotlinlang.org/u/Wasabi375)\
**Post date:** [June 4, 2020, 1:40pm UTC](https://discuss.kotlinlang.org/t/override-class-parameter-type/17960/2 "2020-06-04T13:40:10Z")

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> [@Oleg](#):
>
> and I created two generic classes for this

No you haven’t. Your classes aren’t generic. They don’t have a type parameter. If you want to make `Response` generic you have to do something like

```kotlin
open class Response<T>(
    val code: Int,
    val error: ResponseError,
    var result: T?
)

```

`T` is a type parameter in this case. Inside your class you can use it like any other type(with some small exceptions)  
Now whenever you use `Response` you have to specify which type to use for `T`.

```kotlin
val foo = Response<String>(0, error, "test")

```

or if you want to create your token response class

```kotlin
class TokenResponse(
    code: Int,
    error: ResponseError, 
    result: String?
): Response<String>(code, error, result)

```

Also most times you don’t need to write the type between the angle brackets when using a generic type, because kotlin is smart enough to figure it out from context.  
You should take a look at [https://kotlinlang.org/docs/reference/generics.html](https://kotlinlang.org/docs/reference/generics.html)

---

<div class="post-metadata">

**Author:** ![Oleg](https://sea1.discourse-cdn.com/flex019/user_avatar/discuss.kotlinlang.org/oleg/32/7609_2.png) [@Oleg](https://discuss.kotlinlang.org/u/Oleg)\
**Post date:** [June 4, 2020, 2:30pm UTC](https://discuss.kotlinlang.org/t/override-class-parameter-type/17960/3 "2020-06-04T14:30:35Z")

</div>

I see now, thanks so much!.