How to update individual rows in a 2D array? (Java)

Question

I am trying to make a 2D array that i can dynamically update. Lets say i have a 2D array with 10 rows and 3 columns. I want to add an int value to a specific row, thereby adding an extra column to that row (and only that row) so that it alone would have 4 columns. Here's what i have so far.

public class DynamicArray {
    private int[][] array;
    private int size;

    public DynamicArray(int initialSize) {
        array = new int[10][initialSize];
        size = 0;
    }

    public int get(int j) {
        return array[0][j];
    }

    public int getSize() {
        return size;
    }

    public void put(int N) {
        if (size < array[0].length)
            array[0][size] = N;
        else // need to create a bigger array
        {
            int[][] temp = new int[10][2 * size];
            for (int i = 0; i < array.length; i++)
                for (int j = 0; j < array[i].length; j++)
                    temp[i][j] = array[i][j];
            temp[0][size] = N;
            array = temp;
        }
        size = size + 1;
    }

    public static void main(String[] args) {
        DynamicArray da = new DynamicArray(3);
        da.put(2);
        da.put(1);
        da.put(3);
        da.put(1);
        da.put(4);
        da.put(5);
        for (int i = 0; i < da.getSize(); i++) {
            for (int j = 0; j < 9; j++) {
                System.out.print((da.get(i) + "\t"));
            }
            System.out.println("\n");
        }
    }

}

The problem is that with this code the program adds the new value to each row instead of only the one specified (in this case row 0). How could I fix this?

Additionally, how could i make the program do the opposite as well -> remove a value from an individual row and shorten that row?

Is there a particular reason you don't want to use one of the list types? They would easily solve this problem. — Mic
– Mic, Commented Jan 18, 2015 at 4:23
Mic is right -- ArrayList is good for this sort of thing too. Though if you're hell bent on it; I'd suggest the grueling process of copying the 2-d array to another 2-d array, then re-initializing the original 2-d array to have the proper dimensions, then add to it accordingly with the extra values. — Woodrow
– Woodrow, Commented Jan 18, 2015 at 4:33
@Mic This is for an assignment and we are to use arrays only. Note I am very new to java, just learning and we're only supposed to use what we've covered in the course so far. We havent covered any list types yet. — Pr0metheus
– Pr0metheus, Commented Jan 18, 2015 at 4:35
@Pr0metheus - Okay, that's a fair reason. As Woodrow said, you're looking at defining a new array, copying the existing array into it, and then replacing it. But I think it can be done on a single dimension rather than doing the whole thing. I'll fire up my IDE and try to confirm that for you. — Mic
– Mic, Commented Jan 18, 2015 at 4:45
Sashwat's answer has already addressed pretty much everything I was going to bring up, and he redefines just one row at a time, which is what I was after. So, not much to add to that. I guess the trick is that you don't just have to think of it as a grid of variables. You could view it as an array of arrays as well. — Mic
– Mic, Commented Jan 18, 2015 at 5:15

Keen Sage · Accepted Answer · 2015-01-18 07:01:54Z

In case you just want to add the new element to the new array[0].

public void put(int N) {
    if (size < array[0].length)
        array[0][size] = N;
    else { // need to create a bigger array

        int[] temp = new int[2 * size]; // Temporary create a new array with double size

        // fill the empty array with array[0] existing elements
        for (int i = 0; i < size; i++) {
            temp[i] = array[0][i];
        }

        // Change the array[0] to point to the new array
        array[0] = temp;

        // Add the new element to the new array
        array[0][size] = N;
    }
    size = size + 1;
}

In case you want to put to a specific row number and you should get that as an argument in the put method.

public void put(int N, int rowNum);

You should also change the size element to be a array which will track the size of each row.

int[] size = new int[10];

Accordingly change the size of the row only when that specific row that reached its limit.

Check the code below

public class DynamicArray {
    private int[][] array;
    private int[] size;

    public DynamicArray(int initialSize) {
        array = new int[10][initialSize];
        size = new int[10];
    }

    public int get(int rowNum, int colNum) {
        return array[rowNum][colNum];
    }

    public int getSize(int rowNum) {
        return size[rowNum];
    }

    public void put(int N, int rowNum) {
        if (size[rowNum] < array[0].length)
            array[rowNum][size[rowNum]] = N;
        else { // need to create a bigger array

            int[] temp = new int[2 * size[rowNum]];
            for (int i = 0; i < size[rowNum]; i++) {
                temp[i] = array[rowNum][i];
            }
            array[0] = temp;
            array[0][size[rowNum]] = N;
        }
        size[rowNum] = size[rowNum] + 1;
    }

    public static void main(String[] args) {

        DynamicArray da = new DynamicArray(3);
        da.put(2, 0);
        da.put(1, 0);
        da.put(3, 0);
        da.put(1, 0);
        da.put(4, 0);
        da.put(5, 1);
        da.put(2, 4);
        for (int i = 0; i < 10; i++) {
            for (int j = 0; j < da.getSize(i); j++) {
                System.out.print((da.get(i, j) + "\t"));
            }
            System.out.println("\n");
        }
    }

}

Could you post some code to show me how i would go about implementing that? ( int[] size = new int[]; )

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