Checking to see if a 2d array is jagged

I am finishing up a program but having a bit of trouble with one last aspect.

In this part of the program, I am testing to see if the array is jagged (same number of rows and columns). I want to use a nested for loop to do this but am having trouble with the logic and structure.

For example, the following array is jagged:

1, 2, 3
4, 5, 6
7, 8, 9, 10

And the following array is not:

1, 2, 3
4, 5, 6
7, 8, 9

Can anyone offer guidance on how to do this?

Answer

Start with being clear about what a jagged array is (sticking to 2D arrays as the typical case):

1. Technically a jagged array is an array of (1D) arrays, each of which can have a different length.
2. Often what people mean by “jagged array” (including you I think) is an array with (1D) array elements that do vary in length – i.e. “effectively jagged”.
3. Finally, an array that is technically jagged but has the “same number of rows and columns” is (effectively) a square array.

(Notice that effectively jagged and effectively square arrays are mutually exclusive.)

You do not need nested for loops to check for any of these three conditions:

• Condition 1 is self-evident by virtue of a int[][] declaration.
• Conditions 2 and 3 necessitate one for loop – because you do not need to iterate through the array that contains the potentially different-length arrays and the potentially different-length arrays, just iterate through the former and check the lengths of the latter.

Having said this, consider the following IsJagged and IsSquare implementations and demo with respect to conditions 2 and 3:

public class IsJaggedDemo {
    private static boolean IsJagged(int[][] array) {
        boolean isJagged = false;

        if (array != null) {
            Integer lastLength = null;
            for (int i = 0; i < array.length; i++) {
                if (lastLength == null) {
                    lastLength = array[i].length;
                } else if (lastLength.equals(array[i].length)) {
                    continue;
                } else {
                    isJagged = true;
                    break;
                }
            }
        }

        return isJagged;
    }

    private static boolean IsSquare(int[][] array) {
        boolean isSquare = false;

        if (array != null) {
            for (int i = 0; i < array.length; i++) {
                if (array[i].length != array.length) {
                    break;
                } else if (i != array.length - 1) {
                    continue;
                } else {
                    isSquare = true;
                }
            }
        }

        return isSquare;
    }

    public static void main(String[] args) {
        int[][] a = null;
        int[][] b =
            new int[][] {
                new int[] { 1 }
            };
        int[][] c =
            new int[][] {
                new int[] { 1, 2, 3 },
                new int[] { 4, 5, 6 },
                new int[] { 7, 8, 9 }
            };
        int[][] d =
            new int[][] {
                new int[] { 1, 2, 3 },
                new int[] { 4, 5, 6 },
                new int[] { 7, 8, 9, 10 }
            };
        int[][] e =
            new int[][] {
                new int[] { 1, 2, 3 }
            };
        int[][] f =
            new int[][] {
                new int[] { 1, 2, 3 },
                new int[] { 4, 5, 6 },
                new int[] { 7, 8, 9 },
                new int[] { 9, 8, 7 }
            };

        System.out.printf(
                "a is %1$sjagged and is %2$ssquare.rn",
                IsJagged(a) ? "" : "not ",
                IsSquare(a) ? "" : "not ");
        System.out.printf(
                "b is %1$sjagged and is %2$ssquare.rn",
                IsJagged(b) ? "" : "not ",
                IsSquare(b) ? "" : "not ");
        System.out.printf(
                "c is %1$sjagged and is %2$ssquare.rn",
                IsJagged(c) ? "" : "not ",
                IsSquare(c) ? "" : "not ");
        System.out.printf(
                "d is %1$sjagged and is %2$ssquare.rn",
                IsJagged(d) ? "" : "not ",
                IsSquare(d) ? "" : "not ");
        System.out.printf(
                "e is %1$sjagged and is %2$ssquare.rn",
                IsJagged(e) ? "" : "not ",
                IsSquare(e) ? "" : "not ");
        System.out.printf(
                "f is %1$sjagged and is %2$ssquare.rn",
                IsJagged(f) ? "" : "not ",
                IsSquare(f) ? "" : "not ");
    }
}

If you run the demo, you should see the following output:

a is not jagged and is not square.
b is not jagged and is square.
c is not jagged and is square.
d is jagged and is not square.
e is not jagged and is not square.
f is not jagged and is not square.