HashMaps

HashMaps are unordered collections of key-value pairs that are implemented using a hash table. They offer efficient storage and data retrieval because of how keys are mapped to indices in an array. In Kotlin, a HashMap is represented by the HashMap class.

val map = HashMap<KeyType, ValueType>()

Here, KeyType is the type of the keys in the map, and ValueType is the type of the values.

The types can also be specified when creating an instance of the HashMap class like this:

val map: HashMap<KeyType, ValueType> = HashMap()

The mutableMapOf() function is used to create a mutable HashMap:

A mutable or immutable HashMap is created with the mutableMapOf() or mapOf() methods, respectively:

val mutableMap = mutableMapOf<KeyType, ValueType>()
val immutableMap = mapOf<KeyType, ValueType>()

The following example is a small HashMap of countries and their capitals, and their:

fun main() {
  val locationsMap = HashMap<String, String>()

  locationsMap.put("USA", "Washington D.C.")
  locationsMap.put("India", "New Delhi")
  locationsMap.put("Nigeria", "Abuja")
  locationsMap.put("France", "Paris")

  for((country, capital) in locationsMap) {
    println("$capital, $country")
  }
}

This will print the following output:

Washington D.C., USA
Abuja, Nigeria
Paris, France
New Delhi, India