Understanding Three-Dimensional Arrays

Question

I'm trying to wrap my head around three-dimensional arrays. I understand that they are arrays of two-dimensional arrays, but the book I'm reading said something that confuses me.

In an exercise for the book I'm reading, it asks me to make a three-dimensional array for a full-color image. It gives a small example saying this:

If we decide to choose a three-dimensional array, here's how the array might be declared:

int[][][] colorImage = new int[numRows][numColumns][3];

However, wouldn't it be more effective like this?

int[][][] colorImage = new int[3][numRows][numColumns];

Where 3 is the rgb values, 0 being red, 1 being green, and 2 being blue. With the latter, each two-dimensional array would be storing the color value of the row and column, right? I just want to make sure I understand how to effectively use a three-dimensional array.

Any help will be greatly appreciated, thanks.

Answer 1

Order doesn't matter, and in fact the former form is more readable:

final const int RED = 0;
final const int GREEN = 1;
final const int BLUE = 2;

int[][][] colorImage = new int[numRows][numColumns][3];
//...

int x = getSomeX();
int y = getSomeY();

int redComponent = colorImage[x][y][RED];
int greenComponent = colorImage[x][y][GREEN];
int blueComponent = colorImage[x][y][BLUE];

Answer 2

The order shouldn't matter, so one isn't more effective than the other. The only thing that matters is that whatever accesses colorImage knows which dimension is used for what. Bit more context on multidimensional arrays here.