Only want to fill in top and bottom row of 2D array

Question

I only want to fill in the top and bottom row of an uninitialised array:

for (int i = 0; i < ROWS; i++) {
    for (int j = 0; j < COLUMNS; j++) {
        if (i == 0 || i == (ROWS - 1)) {
            values[i][j] = i;
        }
    }
}

However, when I do so, it fills in all the rows in between with 0:

Why is this the case?

0 is default value to integer arrays in java. It wouldn't make sense to have an array with NULL integers just doesn't. — SharpInnovativeTechnologies, Oct 09 '18 at 04:00

dave · Answer 1 · 2018-10-09T05:18:11.613

2

The default value for any int in Java is zero (0). So any that are left unset will have this value. This is the case whether it's a single int or an array of them. The consequence of this is that the rows which are untouched by your code contain zeroes.

edited Oct 09 '18 at 05:18

answered Oct 09 '18 at 03:59

dave

11,173
5
46
60

Tim Biegeleisen · Accepted Answer · 2018-10-09T05:50:27.983

2

Just access only the top and bottom rows explicitly:

for (int i=0; i < ROWS; i+=ROWS-1) {
    for (int j=0; j < COLUMNS; j++) {
        values[i][j] = i;
    }
}

This avoids iterating every row unnecessarily. Note that the zeroes you are seeing may be the default value for an int array.

edited Oct 09 '18 at 05:50

answered Oct 09 '18 at 04:00

Tim Biegeleisen

451,927
24
239
318

Only want to fill in top and bottom row of 2D array

2 Answers2