Q:

Large foreseeable Sudoku, with 81 integers

I am in the making of a simple Sudoku for my exams at school. I have decided to have only one sudoku. This ones numbers are then shuffled around to make it look like a new one every time. The problem here is that I need to handle 81 integers. Some of them have to be visible, and some not. I can not myself see an easy way to handle these ints with ease, except with arrays, but that didn't go very well.
If you have any suggestions let me know :)

A:

int[][]

Make it a 9x9 array like the visual sudoku.
Any non-visible number can be negated e.g. -5 instead of 5.
To validate the grid as having a solution check the Math.abs(value) (or whatever the absolute function is in your language of choice). Iterate from 1 to 9 in each 'square' and then for each row and column.
This will only let you know that you have a starting arrangement in which you can fill in numbers in a valid way it won't tell you that you can use logically to find that answer exclusively (e.g. an empty grid is valid but has thousands of solutions).

