How to create a ragged array in Java

Question

I wanna create a ragged array (two-dimensional array) that the user inserts the values one at a time. I would usually create them like so:
int[][] array = {{1,2,3}, {6,7}} but I don't know their size beforehand.
How can I create an array like that?

Answer 1

You should initialize a jagged/ragged (same thing) array like this: int array[][] = new int[4][]; Then you can (for example):

    array[0] = new int[5];
    array[1] = new int[5];
    array[2] = new int[5];
    array[3] = new int[5];

Then you can:

for (int i = 0; i < 4; i++){
      for (int j = 0; j < i + 1; j++) {
        array[i][j] = i + j;
      }
}

And if you want to print:

for (int i = 0; i < 4; i++) {
      for (int j = 0; j < i + 1; j++)
        System.out.print(array[i][j] + " ");
      System.out.println();
}

You'll get the output:

0
1 2
2 3 4
3 4 5 6

Of course that if you want to get the input from the user you can substitute any assignment here with Scanner.nextInt();.

Edit after comment: You must specify the size, if you don't wish to do that, then use:

ArrayList<ArrayList<Integer>> array = new ArrayList<ArrayList<Integer>>();