Why does java take so long to initialize two-dimensional arrays, starting with the first dimension, which is large?

Question

I noticed that initializing a 2D array like this

case 1: -

int ar [] [] = new int [10000001][10] ;

it takes more time than its initialization

case 2: -

int ar[] [] = new int [10] [10000001] ;

in case 1, this time is about 4000 ms, but in case 2 it does not exceed 100 ms; why does this big difference exist?

Answer 1

Strictly speaking, Java does not have 2D arrays: instead, it uses 1D arrays sorted into 1D arrays of arrays.

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