Suppose I have a following code:

int[][] arr = new int[1][1];
arr[0] = new int[2];

This is perfectly fine in Java – why? I assumed it allocates memory for a single-element array that can hold single element-array.

If I can pass an array of arbitrary size to arr[0] why am I even able to specify the second dimension size?

Is there any use case when

int[][] arr = new int[1][1]; 

is actually useful over

int[][] arr = new int[1][];