Difference between List and Array types in Kotlin

List and array are two popular collections supported by Kotlin. By definition, both these collections allocate sequential memory location. In this article, we will take an example to demonstrate the difference between these two types of collections.

Attribute	Array	List
Implementation	Array is implemented using Array<T> class	List<T> or MutableList<T> interfaces are used to implement a List in Kotlin
Mutable	Array<T> is mutable, i.e., the values can be changed.	List<T> is immutable in nature. In order to create a mutable list, MutableList<T> interface needs to be used.
Size	Array is of fixed size. It cannot increase and decrease in size.	MutableList<T> do have 'add' and 'remove' functions in order to increase or decrease the size of the MutableList.
Performance	Use it for better performance, as array is optimized for different primitive data types such as IntArray[], DoubleArray[].	Use it for better accessibility in the code. As the size is dynamic in nature, hence good memory management.

Example

In the following example, we will see how we can declare an array and a List in Kotlin and how we can manipulate the values of the same.

fun main(args: Array<String>) {

   val a = arrayOf(1, 2, 3)

   // Printing all the values of array a
   println("The Array contains:")
   a.forEach{
      println(it)
   }


   val names = listOf("stud1", "stud2", "stud3")

   // Printing all the values of list names
   println("\nThe List contains: ")
   names.forEach {
      println(it)
   }


   var days: MutableList<String> = mutableListOf(
      "Monday", "Tuesday", "Wednesday",
      "Thursday", "Friday", "Saturday", "Sunday"
   )

   // Printing all the values of MutableList list
   println("\nGiven Mutable List contains:")
   days.forEach{
      print(it)
   }

   println("\n\nMutable List after modification:")
   days.forEach{
      print(it + ", ")
   }

}

Output

It will generate the following output −

The Array contains:
1
2
3

The List contains:
stud1
stud2
stud3

Given Mutable List contains:
MondayTuesdayWednesdayThursdayFridaySaturdaySunday

Mutable List after modification:
Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday,