Fastest way to read/store lots of multidimensional data? (Java)

Question

I have three questions about three nested loops:

for (int x=0; x<400; x++)
{
    for (int y=0; y<300; y++)
    {
        for (int z=0; z<400; z++)
          


        

Answer 1

Considering that the array is huge, the amount of memory used, the indirections needed (a multidimensional array is a arrays of reference to arrays...), that does not seem at all slow to me. When you switch x and z you are probably trashing the cache.

For comparison, you could store everything in a flat array.... This would improve the storing speed... but then the retrieval would be more complex and much more slow.

int k = 0;
for (int x=0; x<400; x++)
{
    for (int y=0; y<300; y++)
    {
        for (int z=0; z<400; z++)
        {
             // compute and store value
             arr[k++] = val;
        }
    }
}