How to iterate over hashmap in Kotlin?

Question

How to iterate over HashMap in Kotlin?

typealias HashMap<K, V> = HashMap<K, V> (source)

Answer 1

It's not that difficult:

for ((key, value) in map) {
    println("$key = $value")
}

OR
_{(Updated in accordance with @RuckusT-Boom's and @KenZira's information.)}

 map.forEach { (key, value) -> println("$key = $value") }

Answer 2

For the above answer, be careful with Android below N!

map.forEach { key, value -> println("$key = $value") }

reference to Java 8 api which leads to:

Rejecting re-init on previously-failed class java.lang.Class<T>

---

map.forEach { (key, value) -> println("$key = $value") }

is Kotlin feature

Answer 3

Another way that has not been mentioned is:

val mapOfItems = hashMapOf(1 to "x", 2 to "y", -1 to "zz")
mapOfItems.map { (key, value) -> println("$key = $value") }

Answer 4

Use 'for loop' or 'forEach' or 'Iterator'

 fun main(args : Array<String>) {
    val items = HashMap<String, String>()
    items["1"] = "USA"
    items["2"] = "Japan"
    items["3"] = "India"

    //for loop example
    println("\n-- Example 1.1 -- ");
    for ((k, v) in items) {
        println("$k = $v")
    }
    // forEach example
    println("\n-- Example 1.2 --");
    items.forEach { (k, v) ->
        println("$k = $v")
    }

    //Iterator example
    println("\n-- Example 1.3 --");
    val itr = items.keys.iterator()
    while (itr.hasNext()) {
        val key = itr.next()
        val value = items[key]
        println("${key}=$value")
    }

}

Answer 5

Retrieve messages using HashMap in Kotlin.

fun main() {

    // Adding messages to arrayList
    val myMsg = arrayListOf(
        Message(1, "A", "10-02-2022"),
        Message(2, "B", "10-02-2022"),
        Message(3, "C", "11-02-2022"),
        Message(4, "D", "11-02-2022"),
        Message(5, "E", "11-02-2022"),
        Message(6, "F", "12-02-2022"),
        Message(7, "G", "12-02-2022"),
        Message(8, "H", "12-02-2022"),
        Message(9, "I", "14-02-2022"),
        Message(10, "J", "14-02-2022")
    )

    // Getting date wise messages
    val dateWiseMessageList = myMsg.groupBy { it.date }.values
    println("Total sections are ${dateWiseMessageList.size}")

    val myMessageMap = HashMap<Int, List<Message>>()

    // Storing date wise messages to HashMap with Key and Value as multiple messages
    for ((index, value) in dateWiseMessageList.withIndex()) {
        println("the element at $index is $value")
        myMessageMap[index] = value
    }

    // Retrieve messages in date wise section
    for ((key, value) in myMessageMap) {
        println("Section $key data are")
        for (i in value.indices) {
            println(" Id = ${value[i].id} Message = ${value[i].msg} Date = ${value[i].date}")
        }
    }
}

Message data class

data class Message(val id: Int, val msg: String, val date: String)

output