java多维数组符号

Question

To create an length 5 int array, we use the syntax:

 int[] x = new int[5]

To create a 2 dimensional array, an array of int arrays, we say:

 int[][] x = new int[5][];

This creates an array of length 5, which can hold int[] objects.

For this second case, why isn't the syntax this: ?

int[][] x = new int[][5]

After all, 5 defines how many int arrays we can have. Not the size of the int arrays that we're going to put into x.

Answer 1

The array bring declared is the first dimension, so declaring the referenced array size does nothing to allocate the actual array. It would be similar to coding this:

int[] a = new int[];

Answer 2

It would be really weird to have the indices for lookups be different from the indices for construction . So if you had int[][] x= new int[][5] , then you'd look up the elements with x[0..4][foo] , which is just more confusing than the alternative.