KOTLIN: Collection

Sumber: https://www.tutorialspoint.com/kotlin/kotlin_collections.htm

Collections are a common concept for most programming languages. A collection usually contains a number of objects of the same type and Objects in a collection are called elements or items.

The Kotlin Standard Library provides a comprehensive set of tools for managing collections. The following collection types are relevant for Kotlin:

Kotlin List - List is an ordered collection with access to elements by indices. Elements can occur more than once in a list.
Kotlin Set - Set is a collection of unique elements which means a group of objects without repetitions.
Kotlin Map - Map (or dictionary) is a set of key-value pairs. Keys are unique, and each of them maps to exactly one value.

Kotlin Collection Types

Kotlin provides the following types of collection:

Collection or Immutable Collection
Mutable Collection

Kotlin Immutable Collection

Immutable Collection or simply calling a Collection interface provides read-only methods which means once a collection is created, we can not change it because there is no method available to change the object created.

Collection Types	Methods of Immutable Collection
List	listOf()
listOf<T>()
Map	mapOf()
Set	setOf()

Example

fun main() {
    val numbers = listOf("one", "two", "three", "four")
    
    println(numbers)
}

When you run the above Kotlin program, it will generate the following output:

[one, two, three, four]

Kotlin Mutable Collection

Mutable collections provides both read and write methods.

Collection Types	Methods of Immutable Collection
List	ArrayList<T>()
arrayListOf()
mutableListOf()
Map	HashMap
hashMapOf()
mutableMapOf()
Set	hashSetOf()
mutableSetOf()

Example

fun main() {
    val numbers = mutableListOf("one", "two", "three", "four")
    
    numbers.add("five")
    
    println(numbers)
}

When you run the above Kotlin program, it will generate the following output:

[one, two, three, four, five]

Note that altering a mutable collection doesn't require it to be a var.

Quiz Time (Interview & Exams Preparation)

Q 1 - Which of the following is true about Kotlin Collections?

A - Kotlin provides mutable and immutable collection

B - List, Set and Map are Kotlin Collections

C - Kotlin Map can store values in Key-Value pairs

D - All of the above

Q 2 - What will be the output of the following program:

fun main() {

   val numbers = listOf("one", "two", "three", "four")
   
   numbers = listOf("five")

} A - This will print 0

B - This will raise just a warning

C - Compilation will stop with error

D - None of the above

Q 2 - Which statement is not correct?

A - Kotlin List can have duplicate values

B - Kotlin Set can not have duplicate values

C - Immutable collection does not provide methods to change/update the collection.

D - Kotlin does not provide collection types: sets, lists, and maps

Referensi

• https://www.tutorialspoint.com/kotlin/kotlin_collections.htm