Careeroza

Maps

Key-Value Pairs

Example

A Map stores key-value pairs. Keys are unique. "key" to value creates a pair. mapOf keeps insertion order.

fun main() {
    val prices = mapOf("Dosa" to 60, "Idli" to 40, "Vada" to 30)
    println(prices)
    println(prices["Dosa"])            // value or null
    println(prices["Pizza"])
    println(prices.getOrDefault("Pizza", 0))
    println(prices.keys)
    println(prices.values)
    println("Idli" in prices)          // checks keys
    println(prices.size)
}

Output

{Dosa=60, Idli=40, Vada=30}
60
null
0
[Dosa, Idli, Vada]
[60, 40, 30]
true
3

Mutable Maps and Iteration

Example

mutableMapOf lets you add, update and remove entries. Loop with destructuring (key, value).

fun main() {
    val cart = mutableMapOf<String, Int>()     // item -> quantity
    cart["Dosa"] = 2
    cart["Coffee"] = 1
    cart["Dosa"] = 3                           // update
    cart["Vada"] = cart.getOrDefault("Vada", 0) + 1
    cart.remove("Coffee")

    for ((item, qty) in cart) {
        println("$item x $qty")
    }
    println(cart)
}

Output

Dosa x 3
Vada x 1
{Dosa=3, Vada=1}

Note: map[key] returns a nullable type (Int?) because the key might be missing. Use getOrDefault, ?: or getValue (throws if missing).