Kotlin 2d Array initialization

Question

Please take a look at my 2D-Array-Initialization. The code works.

class World(val size_x: Int = 256, val size_y: Int = 256) {

  var worldTiles = Array(size_x, { Array(size_y, { WorldTile() }) })

    fun generate() {
      for( x in 0..size_x-1 ) {
          for( y in 0..size_y-1 ) {
              worldTiles[x][y] = WorldTile()
          }
      }
  }
}

The problem is that it runs the initialization twice. Basically I want to instantiate the WorldTile-Object in the generate() function. So Line 3 shouldn't call "new WorldTile" there. How can I do that?

Also is that the proper Kotlin way of traversing a 2d-Array?

Aren't you already initializing it here: Array(size_x, { Array(size_y, { WorldTile() }) })? — Mibac
– Mibac, Commented Jul 19, 2017 at 19:44
Yes and that is what I want to avoid :) I just wish to define the type there, not initialize it. Maybe I need to add a few parameters to WorldTile later, have those calculated in the for-loop. — Khufu
– Khufu, Commented Jul 19, 2017 at 19:49
As far as I know you'd need a nullable array for that and then you'd use null instead of WorldTile() in Array(..., { /*here*/}) — Mibac
– Mibac, Commented Jul 19, 2017 at 19:50

A-Sharabiani · Accepted Answer · 2019-02-27 02:16:20Z

14

To initialise all to a fixed value:

// A 6x5 array of Int, all set to 0.
var m = Array(6) {Array(5) {0} }

To initialise with a lambda:

// a 6x5 Int array initialise i + j
var m = Array(6) { i -> Array(5) { j -> i + j } }

Another way: Here is an example of initialising a 2D array of Float numbers (3 by 6):

var a = Array(3) { FloatArray(6)} // define an 3x6 array of float numbers
for(i:Int in 0 until a.size) {
    for(j : Int in 0 until a[i].size) {
        a[i][j] = 0f // initialize with your value here.
    }
}

edited Feb 27, 2019 at 2:16

answered Feb 11, 2019 at 23:53

A-Sharabiani

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Pixel Elephant · Accepted Answer · 2017-07-19 19:56:41Z

13

You can make worldTiles a lateinit property, and do all the initialization in the generate function:

class World(val size_x: Int = 256, val size_y: Int = 256) {

  lateinit var worldTiles: Array<Array<WorldTile>>

  fun generate() {
    worldTiles = Array(size_x, {
        Array(size_y, {
            WorldTile()
        })
    })
  }
}

If you try to access worldTiles before calling generate you will get an exception warning that it hasn't been initialized yet.

edited Jul 19, 2017 at 19:56

answered Jul 19, 2017 at 19:55

Pixel Elephant

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chengxuncc · Accepted Answer · 2018-10-14 18:36:45Z

3

val twoDimStringArray= arrayOf(
    arrayOf("first","second"),
    arrayOf("foo"),
    arrayOf("bar","great kotlin")
)
for (i in twoDimStringArray){
    for(j in i){
        println(j)
    }
}

first
second
foo
bar
great kotlin

edited Oct 14, 2018 at 18:36

answered Oct 14, 2018 at 18:28

chengxuncc

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FreddicMatters · Accepted Answer · 2022-07-25 21:19:10Z

1

A bit late but could help to somebody if is working with strings

//init 2d array with a fixed size: 
 var data2 = Array<Array<String>>(2) { arrayOf()}
// fill the 2d array
        data2[0] = arrayOf("123","Freddy x","27")
        data2[1] = arrayOf("124","Elon y","45")

cheers!

answered Jul 25, 2022 at 21:19

FreddicMatters

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