How to edit an array from another class in Java

Question

I have created a 2d array (used as a playing board) and in another class I want to take my array and be able to perform operations on it.

My array definition (in class PlayingBoard):

public char[][] myGrid = new char[12][12];

Now I want to manipulate this array from other classes in my project. I tried to call this grid in the class it was not defined in

int i, j;
for(i = 0; i < 12; i++) {
    for(j = 0; j < 12; j++) {
        PlayingBoard.myGrid[i][j] = 'x';
    }
}

I get the error:

Non-static variable myGrid cannot be referenced from static context

How can I reference, edit, and operate on myGrid from this second class?

Seem to have a minor mixup in the declaration - is this supposed to be an `int` array or a `char` array? It looks like it should be `char` — JonK, Aug 20 '14 at 11:50

score 7 · Accepted Answer · edited Aug 20 '14 at 15:28

7

You must change one of the two things:

declare myGrid as static

public static char[][] myGrid = new char[8][8];

access myGrid via an object instance:

PlayingBoard pb = new PlayingBoard();
int i, j;
for(i = 0; i < 12; i++) {
    for(j = 0; j < 12; j++) {
        pb.myGrid[i][j] = 'x';
    }
}

edited Aug 20 '14 at 15:28

p.s.w.g

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answered Aug 20 '14 at 12:41

twester

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Jeff Watkins · Answer 2 · 2014-08-20T12:55:07.760

The answers point to the use of a static array and this makes me feel sad from an OO point of view.

How about ensuring your playing board has a properly encapsulated structure, with an "addPiece" method?

PlayingBoard myBoard = new PlayingBoard();

int i, j;
for(i = 0; i < 12; i++) {
    for(j = 0; j < 12; j++) {
        myBoard.addPiece(i,j, 'x');
    }
}

Even then, if your pieces themselves are "smart", you'll want to create an object that wraps them rather than just storing a char.

public PlayingPiece[][] _board = new PlayingPiece[8][8];

Also, you're using 12 in the loop but 8 in the initialisation, so expect an IndexOutOfBounds exception.

Thanks for pointing out my mistake, I was only updating the question though.. I wanted it to be useful for whoever else got this problem rather than the mess it was! — LeonH, Aug 20 '14 at 12:52

How to edit an array from another class in Java

2 Answers2