It’s very easy to work with Maps in Kotlin, you can see for yourself in the following examples.

val months = hashMapOf("January" to 1) // (1)
months["February"] = 2                 // (2)
months["March"] = 3

(1) You can simply use the hashMapOf constructor function to declare and initialize the map. There’s no need to provide the type parameter (you still can if you want to, but why bother), the type is inferred from the constructor arguments (2) Adds a new key and value to the map

Another way to create a Map is shown below

val snapshot: MutableMap<String, Int> = months

The variable snapshot is declared to be a MutableMap (pretty much like what we did with hashMapOf. And then, we assigned the months Map object to the snapshot variable. Were not creating a new Map object here, snapshot is essentially months also, they are both pointing to the same Map object.

You can get to the items in the Map this way

println(months["January"]) // prints 1
println(snapshot["March"]) // prints 3

You can traverse the Map this way

months.forEach { println(it) }

Remember that it is the implicit parameter in a lambda. If you want to explicitly work with keys and values of the Map, you can do it like this

months.forEach { k, v -> println("$k | $v") }

Where k is the key and v is the value.

Learn Android Studio 3 with Kotlin
Learn Android Studio 3 with Kotlin

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