Java: Declaring a multidimensional array without specifying the size of the array ( eg. new int[10][] )

Question

I\'ve been trying to figure out what exactly is happening here. I\'m just trying to figure out what the 2 lines are doing that I\'ve commented on below. I found this program

Answer 1

It makes more sense if you think of a multidimensional array as an array of arrays:

int [][] tri = new int[10][]; // This is an array of 10 arrays

tri[r] = new int[r+1]; // This is setting the r'th array to
                       // a new array of r+1 ints