Kotlin - Storing and reading an array in hashmap

Question

Noob to Kotlin. I have a hashmap and which would hold an array for one of it's keys. However when I read the value for that key, Kotlin is not recognizing it as an array.

My hashmap:

var myHashMap = hashMapOf("test" to arrayOf<HashMap<String, Any>>())

Reading the array:

var testString = "__ ${myHashMap["test"].count()} __"

I am getting type mismatch error when I try to read the value. I am storing the array in hashmap in incorrect way?

My hashmap is of type HashMap. I am just specifying the type for the value now and will be storing the actual values dynamically later.

So later when I read myHashMap["test"], I would be expecting something like ["Hello": "World", "ABC": 3]

Edit: Adding my solution

I tried this and it worked for now, but checking if there is a better solution.

    var tests = task["test"] as ArrayList<HashMap<String, Any>>
    var testCount = tests.count()

Also if I want to keep adding values to myHashMap["test"] for now I am storing the existing values into var, adding new onto it and then passing it out to myHashMap["test"].

tests.add(someHashMap)
myHashMap["test"] = tests

Any quicker way to achieve this?

Venkatesh-Prasad Ranganath · Accepted Answer · 2019-05-17 22:57:42Z

1

By type mismatch, are you referring to the following error?

error: only safe (?.) or non-null asserted (!!.) calls are allowed on a nullable receiver of type Array<kotlin.collections.HashMap<String, Any> /* = java.util.HashMap<String, Any> */>?

If so, you should change the expression to "__${myHashMap["test"]?.count()}__" or "__${myHashMap["test"]!!.count()}__" as myHashMap["test"] can evaluate to null.

answered May 17, 2019 at 22:57

Venkatesh-Prasad Ranganath

1,91614 silver badges20 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Dirk Bolte · Accepted Answer · 2019-05-18 12:38:04Z

If you want myHashMap["test"] to return ["Hello": "World", "ABC": 3], this should be a map. A way of entering it can be:

mapOf("test" to mapOf("Hello" to "World", "ABC" to 3))

That might also be the reason for your type mismatch error. When defining it as above, the result would be:

var testString = "__ ${myHashMap["test"]!!.count()} __" // -> 2

hashMapOf("test" to arrayOf<HashMap<String, Any>>()) would result into something like:

{
  "test": [
    { "Hello": "World" },
    { "ABC": 3 }
  ]
}

While mapOf("test" to mapOf("Hello" to "World", "ABC" to 3)) would result in something like this:

{
  "test": {
    "Hello": "World",
    "ABC": 3
  }
}

As background: "Hello" to "World" is an entry of a map. You can add multiple ones in mapOf which are then concatenated to a complete may. Your code would look like you would build an array of maps of which each one just has a single entry.

WRT your update: if you want to have a map in the map, you can also write it like this:

myHashMap["test"] = mapOf("Hello" to "World", "ABC" to 3)

If you want to add keys later on, you should also use mutableMapOf instead. Otherwise myHashMap["newTests"] = ... wouldn't work.

Shradha Sangtani · Accepted Answer · 2019-05-18 15:46:08Z

In the example you mentioned here, var testString = "__ ${myHashMap["test"].count()} __"

You are getting error because myHashMap["test"] could be null and in that case .count() would throw NullPointerException.

Example - Here you created the hashmap with key "test" and tried to access the same. Try running this -

println(myHashMap["dummy"]) // Output - null

Since kotlin is null safe, if the object is nullable, it is necessary to one of the following null safe assertions.

!! -> This means that you don't care even if object is null and you still want .count() to be called.

Example - myHashMap["dummy"]!!.count() Result here would be NullPointerException

? -> This means do not want to call count() if in case myHashMap["dummy"] returns null.

Example - myHashMap["dummy"]?.count() Result here would be null

Collectives™ on Stack Overflow

Kotlin - Storing and reading an array in hashmap

3 Answers 3

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related