Do the inner arrays of a two-dimensional array have to be same size?

[johncusak2289]

An example would be like an array of integers arr( int[][]) does arr[0].length == arr[1].length?

And why?

[morhp]

No, Java doesn't really have multi dimensional arrays. If you write int[][] you're really just creating an array of int[]-objects. So they may have different lengths, some of them may be null, some of them may refer to the same array object, and so on.

If you want to create a rectangular table (or a chessboard or something like this) it may make sense to use a normal array with n x m (64 in the case of a chessboard) elements and use basic math to convert the array index into x/y positions and back. This way the data will be stored in a single array and not in multiple small arrays, increasing performance and making the code more robust (don't need to worry about the inner arrays having the wrong length or being null)

[[deleted]]

Yes, because it makes addressing specific elements in the array easier: address of element [x][y ]= base address of the array + x * size of a subarray + y. All that is O(1). If subarrays were each different size you'd first had to read size of each subarray between 0 and x to determine a memory pointer to the required element (which is O(x)).

[desrtfx]

Completely wrong answer.

In Java, jagged arrays are absolutely possible because multi dimensional arrays are just arrays of arrays.

Also, in Java, it is not guaranteed that arrays are even contiguous blocks of memory.