Arrays performance - 1d vs 2d

Question

Which solution is faster:
int[][] tab = new int[100][100];
tab[x][y] = c;or:
int[] tab = new int[10000];
tab[y*100+x]=c;I know that the second solution is recomended, but it requires one multiplication.
In the first solution compiler can store pointers to second dimension table in first dimension. Pointers have size of 2^n. Integers in second dimension are also of size 2^n. So theoretically compiler may produce byte code that will need no multiplication but only very fast bit-shift operations.
My question is - how does the compiler cope with 2d arrays.
I'm posting my question here because I don't understand bytecode so well. I'm looking for theoretical answer, not benchmark result for specific mobile device.

Answer 1

If I understand right, the problem with that code for the distance matrix is that I dont want to recalculate every row with each iteration, just merge 2 rows from the original distance matrix into 1...and also I cant pick and choose which rows I am merging. There is another function that tells me which rows I have to merge. I could do it with a regular 2d array, but then I need to either shift all the rows each time i merge/remove a row, or I have to keep track of which rows in the matrix i am still using...that would be more complicated than just doing an arrayList of arrayLists I think.
Thanks for the pointer on the arrayList of arrayLists....i'm gonna try to use that for the distanceMatrix. Do you think I lose anything (efficiency or memory) by implementing the 2d arrays the way I have, rather than the arraylist for the expressionMatrix?