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?

Answer 1

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.

Answer 2

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.
    }
}