Why 'null' and NullPointerException is occurring?

import java.util.Arrays; public class Program { public static void main(String[] args) { // int[][] a = new int[2][3]; // is shortcut to int[] array1 = {0,0,0}; int[] array2 = {0,0,0}; int[][] a = {array1, array2}; System.out.println( Arrays.deepToString(a)); // int[][] aa = new int[2][]; // is shortcut to int[][] aa = {null, null}; System.out.println( Arrays.deepToString(aa)); } }

3rd example creates a[null, null] null[0] throws Exception

Yes please any one explain

Please explain more

Tysm

In first There's 2 row and at Every row 3 column But in second there's 2 row but no column so There's like this {{null,null},{null,null}}; ?

aa is internally first array of Objects int[], if there are not elements, default value is null not empty objects Object[] b = new Object[2]; System.out.println( Arrays.toString(b)); // [null, null] // compare to this Object[] d = new Object[2]; Object c1 = new int[3]; Object c2 = new int[3]; d[0] = c1; d[1] = c2; System.out.println( Arrays.deepToString(d)); // [[0, 0, 0], [0, 0, 0]]

> ".. in second there's 2 row but no column" by [2][] length of "column" is not specified, but you expect length 2 {{null,null},{null,null}}; // wrong row = {{column1},{column2}};

Why not 0 earlier there's 0 here's null how can I know where's 0 or where's null...

for int is default 0 for Object is default null array int[] is internally Object

Then what's the difference in example num 2) and no 3) both have new and int keyword then num 2) keyword have 0 and num 3) have null....

you need understand it is not simple one 2D data type, like matrix(x,y) with same elements. this implementation is complex of 1D arrays where one has different type of elements

Ok, thank you