Learn Kotlin (Part 2) - Array, Collection and Range

December 10, 2018

Post Series:

Part 1: Hello world and Basic Data Types

Part 2: Array, Collection and Range

Part 3: Control Flow

Part 4: Function

Part 5: Class

In this post we will discuss about the Array, Collection and Range in Kotlin.

Array

In Kotlin, we can create array using two different ways. First one is by using arrayOf() function and next one is by using Array() constructor.

Using arrayOf() function

val accountInfo = arrayOf("Sudeep", 34000)

The accountInfo array is of type Array<Any>. It holds array with two different types of element String and Int, next there are functions like intArrayOf(), charArrayOf(), booleanArrayOf(), longArrayOf(), shortArrayOf(), byteArrayOf().

The two different types of element String and Int, next there are functions like intArrayOf(), charArrayOf(), booleanArrayOf(), longArrayOf(), shortArrayOf(), byteArrayOf().

For example using intArrayOf(3,4,5,6) make an array of type integer with the given numbers. If you try of push some other types of data into the int array then it will throw compile error.

Alternatively you can use arrayOf<Int> instead of intArrayOf.

val num1 = arrayOf<Int>(3,4,5,6)
val num2 = intArrayOf(3,4,5,6)

Using Array() constructor

Another way of making array is by using Array() constructor. This function takes two parameter, first one is the size of the array and next one is the lambda function to create the values.

val numbersArray = Array(5, { i -> i * 3 })

Collections : List, Set, Map

In kotlin, you can either create mutable or immutable collections. Collections include list, set and map in kotlin.

List

To create immutable list we use the following syntax:

val iMutNumbers: List<Int> = listOf(3,4,5,6)

You cannot edit this list afterwards, if you want to make the list which you can edit later then you should create the mutable list. We use the following syntax to create mutable list:

val mutNumbers: MutableList<Int> = mutableListOf(1,3,4,5)

// You can add item to this list by using add function
mutNumbers.add(9)

Similarly, we can create list of String, Boolean, long and so on.

We can use emptyList() function to create immutable list:

val emptyList: List<String> = emptyList<String>()

Next we have listOfNotNull() function to create list with non-null element.

arrayListOf() creates a mutable list.

Sets

It is an unordered collections of unique element. One of the way to create set is by using setOf() function.

val mixedTypeSet = setOf(4,5,"Pokhara")
val intOnlySet: Set<Int> = setOf(3,4,5,6)
// This creates immutable set

Another way to create set which is mutable is using hashSetOf() function.

val intsHashSet: java.util.HashSet<Int> = hashSetOf(1, 2, 6, 3) intsHashSet.add(5)
intsHashSet.remove(1)

sortedSetOf() creates mutable set which is sorted by using operator.

linkedSetOf() maintains the order in which the items are inserted in the set. It is also mutable.

mutableSetOf() creates the mutable set which is equivalent to Java LinkedHashSet.

Map

Map is the data type which store keys and value pair. All the keys are unique for each of the value. mapOf creates immutable map.

val countryCallingCode: Map<Int, String> = mapOf(977 to "Nepal", 1 to "United States", 61 to "Australia")
for ((key, value) in countryCallingCode) {
    println("The calling code of $value is $key")
}

// It can also be accessed like array
println(countryCallingCode[977])

we can use mutableMapOf() function in order to create the mutable map.

hashMapOf() creates mutable hash map. Hash map class uses a hash table to implement the Java map.

linkedHashMap() stores the data in the order in which they were inserted.

sortedMapOf() stores the data in sorted order.

Range

Range is special data type in kotlin. For example:

var numOneToFive = 1..5

for(i in numOneToFive) {
    print(i)
}

Similarly works for character.

var alphabets = 'a'..'g'

for(i in alphabets) {
    print(i)
}

In the range the starting and the ending values are inclusive. We can use rangeTo() function instead of ..

val oneToFive: IntRange = 1.rangeTo(5)

Next we can use downTo() function to make list of numbers starting from higher to lower range.

val tenToOne = 10.downTo(1)

We can also make a range using some gap. For example to create the range of numbers 1,3,5,7,9 we can use step keyword.

val oneToTenStep = 1..10 step 2

Lastly, if we want to check if a element in inside the range we can use in keyword.

if(4 in tenToOne) {
 print("4 exists in the range.")
}

So, this is all for this post. We learned about Arrays, collection and range in kotlin. We will dive more into Kotlin in the further post.