Syntax for creating a two-dimensional array

Question

Consider:

int[][] multD = new int[5][];
multD[0] = new int[10];

Is this how you create a two-dimensional array with 5 rows and 10 columns?<

Answer 1

Actually Java doesn't have multi-dimensional array in mathematical sense. What Java has is just array of arrays, an array where each element is also an array. That is why the absolute requirement to initialize it is the size of the first dimension. If the rest are specified then it will create an array populated with default value.

int[][]   ar  = new int[2][];
int[][][] ar  = new int[2][][];
int[][]   ar  = new int[2][2]; // 2x2 array with zeros

It also gives us a quirk. The size of the sub-array cannot be changed by adding more elements, but we can do so by assigning a new array of arbitrary size.

int[][]   ar  = new int[2][2];
ar[1][3] = 10; // index out of bound
ar[1]    = new int[] {1,2,3,4,5,6}; // works