JAVA objected 2D array ,Can't set the element in array nor call the function in it

Question

i'm trying to create an minesweeper game using this Class Diagram I'm stuck here for 2 hours and can't find any solution to it,while i'm trying to call the function in the GridData class,the NullPointerException always heppen,Also i can't change the element in an array, Anyone has a suggestion ?

public GridData[][] board ;

public BomberGame(int boardSize,int bombNo){

int i = 0;
int j = 0;
if(boardSize < 3)
    board = new GridData[3][3] ;
else
    board = new GridData[boardSize][boardSize];


 for (i = 0; i < boardSize; i++)
    {
        for (j = 0; j < boardSize; j++)
        {
            //board[i][j]BomberGame = 0 ;// here is the problem i can't mess with any element in array
            board[i][j].setIsOpen(true); // after doing NullPointerException occur
            board[i][j].gridIsOpen();
            System.out.print(board[i][j]+" ");
        }
        System.out.println("");
    }

}

Output

null null null
null null null
null null null

Class Diagram

Answer 1

Doing new GridData[3][3]; will just get you the null array. You'll have to initialize each element in it by doing:

for (i = 0; i < boardSize; i++) {
    for (j = 0; j < boardSize; j++) {
        board[i][j] = new GridData();
    }
}

Once you initialize the array, you can proceed with rest of the code.

Here is the code snippet:

for (i = 0; i < boardSize; i++) {
    for (j = 0; j < boardSize; j++) {
        board[i][j] = new GridData();
        board[i][j].setIsOpen(true); 
        board[i][j].gridIsOpen();
        System.out.print(board[i][j] + " ");
    }
    System.out.println();
}