Java颠倒数组

Question

I was trying to make a simple TicTacToe game.

Here is the code for the coordination:

for(int i=0;i<3;i++){
    for(int j=0;j<3;j++){
        buttons[i][j] = new XOButton();
        // if((i + j) % 2 != 0){
            buttons[i][j].setText(i + "," +j);
        // }
        p.add(buttons[i][j]);
    }
}

Currently, the coordination is from top the bottom, like this:

0,0 0,1 0,2
1,0 1,1 1,2
2,0 2,1 2,2

However, I want it to be from bottom to top like this:

2,0 2,1 2,2
1,0 1,1 1,2
0,0 0,1 0,2

I tried to fix it by changing the value of i and j in the loop like this:

for(int i=3;i>0;i--){
    for(int j=3;j>0;j--){
        buttons[i][j] = new XOButton();
        // if((i + j) % 2 != 0){
            buttons[i][j].setText(i + "," +j);
        // }
        p.add(buttons[i][j]);
    }
}

However, It did not work. It says

Exception in thread 'main' java.lang.ArrayIndexOutOfBoundsException:

I tried to think of the cause of this problem, is it because I have to add date into arrays before the array[3][3]? for example, array[0][0] ~ array[2][3] all have to be filled with data first?

Any help would be appreciated.

Answer 1

You are using indices outside the bouds of the array. Array's indexes in java go from zero to length of the array minus one.

To avoid this kind iof problems you could loop on the size of the array buttons.length-1 and buttons[i].length-1

for(int i=buttons.length-1;i>=0;i--){
    for(int j=buttons[i].length;j>=0;j--){
        buttons[i][j] = new XOButton();
        // if((i + j) % 2 != 0){
            buttons[i][j].setText(i + "," +j);
        // }
        p.add(buttons[i][j]);
    }
}

Answer 2

for(int i=7;i>=0;i--){
   for(int j=0;j<8;j++){
       buttons[i][j] = new XOButton();
       // if((i + j) % 2 != 0){
           buttons[i][j].setText(i + "," +j);
       // }
       p.add(buttons[i][j]);
    } 
}

Answer 3

The obvious answer seems to be that you start at i=8 instead of i=2. This means that on the first pass of the loops i=8 and j=8 and buttons[8][8] is obviously out of bounds.

Also, your break condition should be i>=0 or else i will never be equal to 0 (and the index of your arrays are from 0 to 2).

Answer 4

You are probably better off leaving your iterators i and j the way they were, and doing some math when setting the text of your coordinates. The way arrays work in Java, there is not a whole lot you can do to actually restructure the way they are stored, but you can certainly structure your mental image of how it is stored.

for(int i=0;i<3;i++){
    for(int j=0;j<3;j++){
        buttons[i][j] = new XOButton();
        // if((i + j) % 2 != 0){
            buttons[i][j].setText((buttons.length - i) + "," + (buttons[i].length - j));
        // }
        p.add(buttons[i][j]);
    }
}

That should get your arrays set up so they have the text laid out in the fashion you describe. Notice I used (buttons.length - i) and (buttons[i].length - j) to "switch" the coordinates to count down. This is just a trick to avoid using undefined constants in the code, but you could technically replace both with 3 .