Why 'null' and NullPointerException is occurring?

Question

1)

int[] a =new int[3];
Sop(a); //[|@3e25a5
Sop(a[0]); //0

2)

int[][] a =new int[2][3];
Sop(a); //[|@3e25a5
Sop(a); //[|@19821f
Sop(a[0][0]); //0

3)

int[][] a =new int[2][];
Sop(a); //[|@3e25a5
Sop(a[0]); //null
Sop(a[0][0]); //R.E:NullPointerException

Answer 1

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));
}
}

Answer 2

3rd example creates
a[null, null]

null[0] throws Exception

Answer 3

Yes please any one explain

Answer 4

Please explain more

Answer 5

Tysm

Answer 6

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}};

?

Answer 7

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]]

Answer 8

> ".. 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}};

Answer 9

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

Answer 10

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

Answer 11

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....

Answer 12

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

Answer 13

Ok, thank you