In this article , lets discuss about Kotlin Collections

Collections are used to store and manipulate group of objects or data

Ordered Collection is the collection in which the position of each item is fixed Eg: Lists , Array , etc

Unordered Collection is the collection in which the position of each item is not fixed which means order of all elements are not maintained. Eg: Set

Collection Types

Immutable Collection

This collection supports read only functionality and we cannot modify its elements

List

• This is an ordered collection in which elements can be accessed using indices

• Elements can be repeated in list for any number of times

• We cannot perform add/remove operations in this immutable list

  listOf() , listOf<T>()

 val androidOsName = listOf(
        "Upside Down Cake",
        "Vanilla Ice Cream",
        "Tiramisu",
        "Snow Cone",
        "Red Velvet Cake"
    )

    for (name in androidOsName){
        println(name)
    }

Set

• This is an unordered collection in which elements cannot be duplicated

• Set is collection of unique elements

• We cannot perform add/remove operations because of immutable collection setOf()

 val android14Info  = setOf(
        "Android 14" ,
        "Upside Down Cake" ,
        14 ,
        34 ,
        "October 4 2023 "
    )

    for (name in android14Info){
        println(name)
    }

Map

• Maps are unordered collection of set of key/value pairs

• Map key are unique and can hold only one value for each key

• Keys are unique but values are duplicated

• Map is used to store logical collection between two objects

• As it is immutable , size is fixed and supports read only access .

  mapOf()

 val androidOsInfo = mapOf(
        13 to "Android 13 - Tiramisu - 13 - 33 - August 15, 2022 " ,
        12 to "Android 12 - Snow Cone - 12 - 31 - October 4, 2021 " ,
        11 to "Android 11 - Red Velvet Cake[24] - 11 - 30 tSeptember 8, 2020 "
    )

    for (info in androidOsInfo) {
        println("${info.key} -> ${info.value}")
    }

Mutable Collection

This collection supports both read and write functionality.

List

• This mutable list supports both read and write operation

• The declared elements in list can be either removed or added

  mutableListOf() , arrayListOf<T>() , ArrayList

 val androidOsName = mutableListOf(
        "Upside Down Cake",
        "Vanilla Ice Cream",
        "Tiramisu"
    )

    // modify item
    androidOsName[0] = "Pistachio Ice Cream"

    // add item
    androidOsName.add("Snow Cone")

    for (name in androidOsName){
        println(name)
    }

Set

• This set supports both read and write

• Set allows us to easily to add/remove elements

• Order of elements are preserved

  mutableSetOf() , hashSetOf()

val androidOsName = mutableSetOf<String>(
        "Upside Down Cake",
        "Vanilla Ice Cream",
        "Tiramisu"
    )

    // add item
    androidOsName.add("Snow Cone")

    // remove item
    androidOsName.remove("Upside Down Cake")

    for (name in androidOsName){
        println(name)
    }

Map

Since this Map is mutable and this supports operations like put, remove , clear ,etc

mutableMapOf() , hashMapOf() and HashMap

val androidOsInfo = mutableMapOf(
        13 to "Android 13 - Tiramisu - 13 - 33 - August 15, 2022 ",
        12 to "Android 12 - Snow Cone - 12 - 31 - October 4, 2021 ",
        11 to "Android 11 - Red Velvet Cake[24] - 11 - 30 tSeptember 8, 2020 "
    )

    // add item
    androidOsInfo.put(10, "Android 10 - Quince Tart[24] - 10 - 29 - September 3, 2019 ")

    // remove item
    androidOsInfo.remove(12)

    for (info in androidOsInfo) {
        println("${info.key} -> ${info.value}")
    }

So finally, I hope I made somebody understand the basics of kotlin collections

Please leave your comments to improve.

Happy and Enjoy coding