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