Android Volley Kotlin: (Mutable)Map<(raw) Any?, (raw) Any?>! vs MutableMap<String, String>

Question

In Android with Kotlin and Volley Library, I am using the below code to put a map into jsonObject.

val params = mutableMapOf<String, String>()
params["key1"] = "value1"
params["key2"] = "value2"
val parameter = JSONObject(params)

This give me the below error:

Java type mismatch expected (Mutable)Map<(raw) Any?, (raw) Any?>! but found MutableMap<String, String>. Use explicit cast

1. Why do I need explicit cast as params as Map<*, *>
2. What is (Mutable)Map?
3. What are differences between (Mutable)Map and MutableMap?

Answer 1

The JSONObject constructor takes a Map with raw types (the generics are not specified). As such you should supply a map that can be of Any type :

val params = mutableMapOf<Any?, Any?>()
    params["key1"] = "value1"
    params["key2"] = "value2"
    val parameter = JSONObject(params)

The warning (Mutable)Map<(raw) Any?, (raw) Any?> is showing the Java parameter argument - stating it can expect either a Map or MutableMap, as you are calling Java code from Kotlin - Java won't know if the Map is mutable or immutable. Just to note raw types are not supported by Kotlin, you only encounter this problem if calling Java code.