Creating Conway Game Of Life - Index Out Of Bounds?

The question pretty much says it all. My problem seems to be when adding the neighbours, I am always getting a Index out of Bounds problem. I know this is because the code is reaching for the edge of the table, for example if the column, i = 0 and the statement says to perform i - 1 and return it, then we are going to have a problem.

Similarly with anything like j = 20, j + 1 (as the grid only has 20 spaces). I understand the problem, but I am unsure of how to solve it. I have tried messing around with the if statements, but I continue to get the 'out of bounds' problem...

import javax.swing.*;
public class GameOfLife {
/**
* @param args the command line arguments
*/
public static void main(String[] args) {
int cellChoice = 0;
int newCells = 1;
int generation = 1;
int neighbours = 0;

[Code] .....