convert android hashmap to kotlin

Question

I have a Java HashMap populated as

HashMap<String, Integer> myMMap = new HashMap<String, Integer>();
for (int i = 0; i < objects.size(); ++i) {
    myMap.put(objects.get(i), i);
}

And I'm trying to convert this to Kotlin. I tried the way below, but I'm getting null value in it.

var myMap : HashMap<String, Int>? = null
for (i in objects){
    //myMap?.put(i, objects.indexOf(i))
    myMap?.put("sample", 3)
    System.out.println("myMapInForLoop" + myMap)
}

It prints I/System.out: myMapInForLoopnull.

I've tried using hashMapOf function, but it allows only 1 value, so I cannot put that in myMap.

Answer 1

You can instantiate the HashMap directly. Instead of a for-loop you could then use forEachIndexed for example (if objects is an Array or Iterable).

val myMap = HashMap<String, Int>()
objects.forEachIndexed { index, item ->
    myMap.put(item, index)
    System.out.println("myMapInForLoop" + myMap)
}

In your version of the code you get null, because you assign it to myMap. Also you might have only a single value, because you only set a "sample" key for testing.

Answer 2

Late to the party, but you can also use

val myMap = objects.withIndex().associateTo(HashMap<String, Int>()) {
    it.value to it.index
}

Answer 3

You need to use val myMap = mutableMapOf<String, Int>() if you want to mutate the map within the loop.