output now:-
0
1 2
3 4 5
6 7 8 9





// Array row column print..in 2D Diamontional new print..


        //initilize array create just row, not column
        int [][] num = new int[4][];


        //first row column declare..
        // 0 num row a column thakbe 1 ta.
        // 1 num row a column thakbe 2 ta.


        //row er under a column create,  row num[0] a akta column new int[1]; create korlam.
        num[0] = new int[1];
        num[1] = new int[2];
        num[2] = new int[3];
        num[3] = new int[4];


        //initlize the value.
        int k = 0;

        //create row with every looping 1 add to column with asign to num..
        for (int i =0; i<4; i++){

            for (int j =0; j<i+1; j++){

                // num asign korte hobe 1 , 1 kore barate hobe.

                num[i][j] = k;
                k++;
            }
        }



         // display show this array now...
        for (int i=0; i<4; i++){

            for (int j=0; j<i+1; j++){

                System.out.print(num[i][j]+" ");
            }

            System.out.println();
        }