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Creating arrays

Learn to create arrays with arrayOf and intArrayOf.

Creating arrays

An array is a fixed-size collection. In Kotlin, arrayOf creates an array of any type.

val fruits = arrayOf("apple", "pear", "cherry")
val nums = intArrayOf(3, 7, 2, 5)
println(fruits.contentToString())  // [apple, pear, cherry]

arrayOf makes a general array (Array<String>). intArrayOf makes a specialized array for Ints (IntArray); it uses less memory.

To print an array's contents, use contentToString(); plain println(array) prints an address. Array size does not change after creation.

Array and IntArray

arrayOf and intArrayOf produce different types. arrayOf(1, 2, 3) gives an Array<Int>; intArrayOf(1, 2, 3) gives an IntArray.

val a = arrayOf(1, 2, 3)       // Array<Int>
val b = intArrayOf(1, 2, 3)    // IntArray
println(a[0])  // 1
println(b[0])  // 1

Both use the same access syntax: array[index]. IntArray is primitive-based; it is more efficient for large amounts of numbers.

arrayOf is for complex types (String, objects); intArrayOf is for Ints only.

Practice Create an array and print it

Write a fun main(). Create an array with val fruits = arrayOf("apple", "pear", "cherry"). Print its contents with println(fruits.contentToString()).

Starter code

Main.kt
fun main() {
    // Create an array and print it
}

Sample solution

Main.kt
fun main() {
    val fruits = arrayOf("apple", "pear", "cherry")
    println(fruits.contentToString())
}

Expected output

[apple, pear, cherry]

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 What type of array does arrayOf("a", "b", "c") create?

  • List<String>
  • IntArray
  • String
  • Array<String> Correct answer

Explanation: arrayOf creates an Array<String> of Strings.

2 Complete the arrayOf call

Question 
val fruits = ____("apple", "pear", "cherry")
Answer 
val fruits = arrayOf("apple", "pear", "cherry")

Explanation: arrayOf("apple", ...) creates a String array.

3 Match the array creation forms

Term Meaning
arrayOf(...) General array
intArrayOf(...) Int array
Array<String> String array type
IntArray Int array type

All lessons in Beginner

1 Kotlin basics

  1. What is Kotlin?
  2. Your first program
  3. The main function
  4. Comments
  5. String templates
  6. Summary - Kotlin basics

2 Variables

  1. val and var
  2. Type inference
  3. const
  4. lateinit
  5. by lazy
  6. Summary - Variables

3 Data types

  1. Integer types
  2. Floating-point types
  3. Boolean and Char
  4. String
  5. Any and Unit
  6. Summary - Data types

4 Project: Calculator

  1. Project design
  2. Add and subtract
  3. Multiply and divide
  4. Error handling
  5. Putting it together

5 Operators

  1. Arithmetic operators
  2. Assignment operators
  3. Comparison operators
  4. Logical operators
  5. Elvis operator
  6. Summary - Operators

6 Strings

  1. Creating strings
  2. String templates
  3. String methods
  4. substring
  5. split and replace
  6. Summary - Strings

7 Conditionals

  1. The if statement
  2. else and else if
  3. if expression
  4. when
  5. when expression
  6. Summary - Conditionals

8 Loops

  1. The for loop
  2. The while loop
  3. The do-while loop
  4. Range
  5. break and continue
  6. Summary - Loops

9 Project: Shopping cart

  1. Cart design
  2. Adding items
  3. Calculating totals
  4. Listing the cart
  5. Putting it together

10 Arrays

  1. Creating arrays
  2. Array access
  3. Array size
  4. Array loop
  5. Array methods
  6. Summary - Arrays

11 Lists

  1. Creating lists
  2. List operations
  3. List access
  4. List iteration
  5. List methods
  6. Summary - Lists

12 Maps and Sets

  1. Creating sets
  2. Set operations
  3. Creating maps
  4. Map operations
  5. Map iteration
  6. Summary - Maps and Sets

13 Functions

  1. Defining functions
  2. Return values
  3. Expression body
  4. Default parameters
  5. Named arguments
  6. Summary - Functions

14 Null safety

  1. Nullable types
  2. ?, !! and ?:
  3. let
  4. Null check
  5. lateinit
  6. Summary - Null safety

15 Project: To-do CLI

  1. Task model
  2. Adding tasks
  3. Listing tasks
  4. Completing tasks
  5. Putting it together

16 Advanced string operations

  1. Regex
  2. matches and find
  3. replace
  4. StringBuilder
  5. trim and pad
  6. Summary - Advanced strings

17 Enums

  1. enum class
  2. Enum values
  3. Enum properties
  4. when with enum
  5. Enum and range
  6. Summary - Enums

18 Exceptions

  1. try/catch
  2. throw
  3. finally
  4. try expression
  5. Custom exceptions
  6. Summary - Exceptions

19 Class basics

  1. class
  2. Constructor
  3. Properties
  4. Methods
  5. this
  6. Summary - Class basics

20 Beginner final

  1. Project design
  2. Classes
  3. Collections
  4. Error handling
  5. Putting it together