Adding up values around a specific point in an array in Java

Question

So I have a 2D array which is filled with 1's and 0's. I want to check the neighbours of a specific index in the array, and add their values up.

The first and last rows and columns (aka the 'bordering' values) are special cases as they are not completely surrounded with neighbouring values which means I have to put lots of conditionals to take them into account.

If I only do the first if statement, I get the problem of arrayIndexOutOfBounds. Which makes sense to me as its trying to go to position integerGeneration[-1][-1], for example.

What I have done below works, but its really ugly and I feel there is a "neater" approach to this.

Is there a better way than doing all the special cases on the outer borders of the array in their own else if statements?

// checks the inside box
if ((x > 0 & x < rows - 1) & (y > 0 & y < columns - 1)) {
    for (int i = x - 1; i < x + 2; i++) {
        for (int j = y - 1; j < y + 2; j++) {
            filled = integerGeneration[i][j] + filled;
        }
    }
    filled = filled - integerGeneration[x][y];
    return filled;
// checks the top edge
} else if (x == 0 & y < columns - 1 & y > 0) {
    for (int i = x; i < x + 2; i++) {
        for (int j = (y - 1); j < y + 2; j++) {
            filled = integerGeneration[i][j] + filled;
        }
    }
    filled = filled - integerGeneration[x][y];
    return filled;
// checks the left edge
} else if (y == 0 & x < rows - 1 & x > 0) {
    for (int i = x - 1; i < x + 2; i++) {
        for (int j = y; j < y + 2; j++) {
            filled = integerGeneration[i][j] + filled;
        }
    }
    filled = filled - integerGeneration[x][y];
    return filled;
// checks the top left corner
} else if (x == 0 & y == 0) {
    for (int i = x; i < x + 2; i++) {
        for (int j = y; j < y + 2; j++) {
            filled = integerGeneration[i][j] + filled;
        }
    }
    filled = filled - integerGeneration[x][y];
    return filled;
// checks the bottom edge
} else if (x == rows - 1 & y < columns - 1 & y > 0) {
    for (int i = x - 1; i < x + 1; i++) {
        for (int j = y - 1; j < y + 2; j++) {
            filled = integerGeneration[i][j] + filled;
        }
    }
    filled = filled - integerGeneration[x][y];
    return filled;
// checks the right edge
} else if (y == columns - 1 & x < rows - 1 & x > 0) {
    for (int i = x - 1; i < x + 2; i++) {
        for (int j = y - 1; j < y + 1; j++) {
            filled = integerGeneration[i][j] + filled;
        }
    }
    filled = filled - integerGeneration[x][y];
    return filled;
// checks the bottom right corner
} else if (y == columns - 1 & x == rows - 1) {
    for (int i = x - 1; i < x + 1; i++) {
        for (int j = y - 1; j < y + 1; j++) {
            filled = integerGeneration[i][j] + filled;
        }
    }
    filled = filled - integerGeneration[x][y];
    return filled;
// checks the top right corner
} else if (x == 0 & y == columns - 1) {
    for (int i = x; i < x + 2; i++) {
        for (int j = y - 1; j < y + 1; j++) {
            filled = integerGeneration[i][j] + filled;
        }
    }
    filled = filled - integerGeneration[x][y];
    return filled;
// checks the bottom left corner
} else if (x == rows - 1 & y == 0) {
    for (int i = x - 1; i < x + 1; i++) {
        for (int j = y; j < y + 2; j++) {
            filled = integerGeneration[i][j] + filled;
        }
    }
    filled = filled - integerGeneration[x][y];
    return filled;
} else {
    System.out.println("Error, point out of bounds");
    return -1;
}

That is a lot of code duplication. Why don't you just have the loops iterate over the "surrounding" elements and check the relevant index before trying to access (e.g.: if(x < 0) continue;) — UnholySheep
– UnholySheep, Commented Jan 1, 2017 at 12:05
@UnholySheep Oh, oops. Do you mean something like this? public static int neighbours(int x, int y) { // get the number of filled neighbours int filled = 0; for (int i = x - 1; i < x + 2; i++) { for (int j = y - 1; j < y + 2; j++) { if ((i < 0 | i >= rows) | (j < 0 | j >= columns) | (i == x & j == y)) continue; else filled += integerGeneration[i][j]; } } return filled; } — Sev
– Sev, Commented Jan 1, 2017 at 12:59
oh wow, and im not allowed to edit that D: ` for (int i = x - 1; i < x + 2; i++) { for (int j = y - 1; j < y + 2; j++) { if ((i < 0 | i >= rows) | (j < 0 | j >= columns) | (i == x & j == y)) continue; else filled += integerGeneration[i][j]; } } return filled;` — Sev
– Sev, Commented Jan 1, 2017 at 13:03

skag · Accepted Answer · 2020-05-25 12:30:16Z

2

Check this out:

filled = 0;
for (int i = x - 1; i < x + 2; i++) {
    for (int j = y - 1; j < y + 2; j++) {
        if (i < 0 || i >= rows || j < 0 || j >= columns || i == x || j == y)
            continue;
        filled = integerGeneration[i][j] + filled;
    }
}
return filled;

edited May 25, 2020 at 12:30

user11141611

answered Jan 1, 2017 at 13:43

skag

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6 Comments

Sev Over a year ago

shouldn't it be i==x && j==y?

skag Over a year ago

yeah sorry it was typo

Sev Over a year ago

no worries, was just checking to make sure I understood that correctly :P Thank you very much!

skag Over a year ago

if(i<0 || i>=rows || j<0 || j>=columns || (i==x && j==y))

skag Over a year ago

welcome and you can also upvote the answer if you are satisfied

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