What would be the equivalent in Java of `Array<IntArray>`? I'm trying to store a 2D matrix of ...

# getting-started

[Karlo Lozovina]

What would be the equivalent in Java of Array<IntArray>? I'm trying to store a 2D matrix of ints/floats in a compact way, would this Array of IntArrays be the way to go? Would that be equivalent to int[][]?

[Joffrey]

If you want to be equivalent, yes that's what this is. However, if accesses to this structure are performance sensitive, you might want to consider a 1-dimensional int array instead (using i * width + j indexing to map to 2D). This avoids pointer indirections

[Karlo Lozovina]

yeah, I think I misunderstood how Java lays out int[][] in memory - it's not a one continuous chunk of memory, it's array of pointers to arrays with continous memory?

[Karlo Lozovina]

I thought Java did something Kotlin can't... actually, Java doesn't do it as well (probably will with Valhalla)

[Karlo Lozovina]

I think I'll try going with a one large int[] array and do the indexing myself...

[Karlo Lozovina]

thanks!

[Joffrey]

Yes exactly, Java and Kotlin have the same capabilities in this respect, you have to manually handle your 1D array if you want contiguous memory

[Youssef Shoaib [MOD]]

Just saying, you can very easily create a @JvmInline value class 2DIntArray that under the hood uses a normal IntArray and lays out the 2d matrix in a continuous block of memory so that it's still efficient but all the indexing for getting and setting are hidden away in the value class

[Joffrey]

Of course the smart indexing needs to be abstracted away

[Youssef Shoaib [MOD]]

Yeah I'm just saying that a value class will make that invisible to any consumer of the array

[Tobias Berger]

just a little hint on the side: you could write an extension for the get-operator function on IntArray (or some wrapper class if you prefer) that accepts 2 parameters. Of course this would require you to know the "width" of your matrix, but it could look something like this:

operator fun IntArray.get(x: Int, y: Int) = get(y * width + x)

That way you could call my2DArray[x, y]