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's not lacking, it's basically not setting a specific amount, it isn't required because it can have many fields

and the second line

tri[r] = new int[r+1];

is setting all the fields to not null