How to initialize an array in Kotlin with values

Question

In Java an array can be initialized such as   int numbers     new int    10  20  30  40  50    How does Kotlin s array initialization look like

User · Answer

Old question  but if you d like to use a range   var numbers  IntArray   IntRange 10  50  step 10  toList   toIntArray     Yields nearly the same result as   var numbers   Array 5    i - gt  i 10   10      result  10  20  30  40  50  I think the first option is a little more readable  Both work

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You can create an Int Array like this   val numbers   IntArray 5    10    it   1       5 is the Int Array size  the lambda function is the element init function   it  range in  0 4   plus 1 make range in  1 5   origin function is           An array of ints  When targeting the JVM  instances of this class are     represented as  int         constructor Creates a new array of the specified  size   with all elements      initialized to zero       public class IntArray size  Int                         Creates a new array of the specified  size   where each element is            calculated by calling the specified            init  function  The  init  function returns an array element given            its index                   public inline constructor size  Int  init   Int  - gt  Int             IntArray class defined in the Arrays kt

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I think one thing that is worth mentioning and isn t intuitive enough from the documentation is that  when you use a factory function to create an array and you specify it s size  the array is initialized with values that are equal to their index values  For example  in an array such as this  val array   Array 5    i - gt  i     the initial values assigned are  0 1 2 3 4  and not say   0 0 0 0 0   That is why from the documentation  val asc   Array 5    i - gt   i   i  toString      produces an answer of   0    1    4    9    16

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My answer complements  maroun these are some ways to initialize an array   Use an array  val numbers   arrayOf 1 2 3 4 5    Use a strict array  val numbers   intArrayOf 1 2 3 4 5    Mix types of matrices  val numbers   arrayOf 1 2 3 0 4f    Nesting arrays  val numbersInitials   intArrayOf 1 2 3 4 5  val numbers   arrayOf numbersInitials  arrayOf 6 7 8 9 10     Ability to start with dynamic code  val numbers   Array 5   it 2

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Simple Way   For Integer   var number    arrayOf lt  Int   10   20   30   40  50   Hold All data types  var number   arrayOf 10    string value    10 5

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val numbers  IntArray   intArrayOf 10  20  30  40  50    See Kotlin - Basic Types for details   You can also provide an initializer function as a second parameter   val numbers   IntArray 5    10    it   1        10  20  30  40  50

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You can simply use the existing standard library methods as shown here   val numbers   intArrayOf 10  20  30  40  50    It might make sense to use a special constructor though   val numbers2   IntArray 5     it   1    10     You pass a size and a lambda that describes how to init the values  Here s the documentation          Creates a new array of the specified  size   where each element is calculated by calling the specified     init  function  The  init  function returns an array element given its index      public inline constructor size  Int  init   Int  - gt  Int

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I m wondering why nobody just gave the most simple of answers   val array  Array lt Int gt     1  2  3      As per one of the comments to my original answer  I realized this only works when used in annotations arguments  which was really unexpected for me    Looks like Kotlin doesn t allow to create array literals outside annotations   For instance  look at this code using  Option from args4j library          Option          name    -h           aliases     --help    -             usage    Show this help            var help  Boolean   false    The option argument  aliases  is of type Array lt String gt

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you can use this methods  var numbers Array lt Int gt  size init  var numbers IntArray size init  var numbers  intArrayOf 1 2 3    example  var numbers   Array lt Int gt  5    i - gt  0      init represents the default value   initialize

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Declare int array at global   var numbers  intArrayOf     next onCreate method initialize your array with value  override fun onCreate savedInstanceState  Bundle         super onCreate savedInstanceState      setContentView R layout activity main        create your int array here     numbers  intArrayOf 10 20 30 40 50

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In Kotlin There are Several Ways   var arr   IntArray size     construct with only size   Then simply initial value from users or from another collection or wherever you want   var arr   IntArray size  0      construct with size and fill array with 0 var arr   IntArray size  it     construct with size and fill with its index   We also can create array with built in function like-  var arr   intArrayOf 1  2  3  4  5     create an array with 5 values   Another way  var arr   Array size  0     it will create an integer array var arr   Array lt String gt  size    it      this will create array with  0    1    2  and so on    You also can use doubleArrayOf   or DoubleArray   or any primitive type instead of Int

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intialize array in this way   val paramValueList   Array lt String  gt    arrayOfNulls lt String gt  5

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Kotlin language has specialised classes for representing arrays of primitive types without boxing overhead  for instance     IntArray  ShortArray  ByteArray  etc  I need to say that these classes have no inheritance relation to the parent Array class  but they have the same set of methods and properties  Each of them also has a corresponding factory function  So  to initialise an array with values in Kotlin you just need to type this  val myArr  IntArray   intArrayOf 10  20  30  40  50      or this way  val myArr   Array lt Int gt  5    i - gt    i 1    10      myArr forEach   println it                                      10  20  30  40  50  Now you can use it  myArr 0     myArr 1    myArr 2   - myArr 3

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You can try this    var a   Array lt Int gt  5  0

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In Java an array can be initialized such as   int numbers     new int    10  20  30  40  50    But In Kotlin an array initialized many way such as   Any generic type of array you can use arrayOf    function    val arr   arrayOf 10  20  30  40  50   val genericArray   arrayOf 10   Stack   30 00  40   Fifty     Using utility functions of Kotlin an array can be initialized  val intArray   intArrayOf 10  20  30  40  50

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In Kotlin we can create array using arrayOf    intArrayOf    charArrayOf    booleanArrayOf    longArrayOf   functions   For example   var Arr1   arrayOf 1 10 4 6 15    var Arr2   arrayOf lt Int gt  1 10 4 6 15    var Arr3   arrayOf lt String gt   Surat   Mumbai   Rajkot     var Arr4   arrayOf 1 10 4   Ajay   Prakesh     var Arr5  IntArray   intArrayOf 5 10 15 20

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In this way  you can initialize the int array in koltin    val values  IntArray   intArrayOf 1  2  3  4  5 6 7

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Here s an example   fun main args  Array lt String gt         val arr   arrayOf 1  2  3       for  item in arr            println item             You can also use a playground to test language features

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Worth mentioning that when using kotlin builtines  e g  intArrayOf    longArrayOf    arrayOf    etc  you are not able to initialize the array with default values  or all values to desired value  for a given size  instead you need to do initialize via calling according to class constructor       Array of integers of a size of N val arr   IntArray N      Array of integers of a size of N initialized with a default value of 2 val arr   IntArray N    i - gt  2

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In my case I need to initialise my drawer items  I fill data by below code       val iconsArr   IntArray   resources getIntArray R array navigation drawer items icon      val names   Array lt String gt    resources getStringArray R array navigation drawer items name           Use lambda function to add data in my custom model class i e  DrawerItem     val drawerItems   Array lt DrawerItem gt  iconsArr size  init                               index - gt  DrawerItem iconsArr index   names index         Log d LOGGER TAG   Number of items in drawer is     drawerItems size    Custom Model class-  class DrawerItem var icon  Int  var name  String

[arrays] How to initialize an array in Kotlin with values?

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