Why am I receiving this NullPointerException?

Question

I encounter a NullPointerException on clickCell[r][c] = false; and on new LifeGUI(new LifeModel(x, y, s); and can't fix it. Please explain why this problem occurs and how I may fix it.

Code:

public  LifeModel(int rows, int cols, int cellSize) {
    row = rows;
    col = cols;
    cSize = cellSize;
    for (int r = 0; r < row; r++) {
        for ( int c = 0; c < col; c++) {
            clickCell[r][c] = false;
        }
    }
}

public static void main(int x, int y, int s) {
    new LifeGUI(new LifeModel(x, y, s));        
}

Answer 1

You have to create the array object

boolean [][] clickCell = new boolean[rows][cols];

Add this command before the for loop.

More info here

If clickCell is declared somewhere else, the command should be:

clickCell = new boolean[rows][cols];

Or as GriffeyDog suggests, add the new boolean[rows][cols] at the place where you declare the array, depending on the logic of your program.

Answer 2

You haven't shown where the clickcell array was declared, but likely you have declared it but not initialized it. You may have

boolean[][] clickcell;

but need:

boolean[][] clickcell = new boolean[rows][cols];

where rows and cols represent the size of the array you need.