Enthuware

Dont understand the difference between,
{{0, 1}, {2, 3}, {4, 5}};
and
{ { {0, 1}, {2, 3}, {4, 5} } };

To start with, did you notice the difference in number of opening and closing brackets?

Yes, syntactically, they are different.
So, does that mean to separate dimensions in arrays, we require {}?

Yes, try this - http://stackoverflow.com/questions/1067 ... ay-in-java

BTW, your question is too basic. You should first read a book to learn the basics and then attempt the mock exams. Otherwise, it will not help you much.

kindly explain "int[][] arr2 = {arr, {1, 2}, arr};"
how is this valid?

Again, it is quite basic. You need to go through a book and read a chapter on arrays.
It is not really possible to explain the whole chapter in a post here. Briefly, arr2 is a two dimensional array of ints, so each element of arr2 must be a one dimensional array of ints, which is what {arr, {1, 2}, arr} is doing.

Understood.
Its array of array we are looking at.
We say its 2D array, and elements are 1D.
"," separates each element.
So, the above mentioned elements form only one part of aoa.
But, {1,2}, whats that?
AND
hows {arr, {1, 2}, arr} different from {{0, 1}, {2, 3}, {4, 5}}

Please go through the link I gave you above. Read all the answers there.

Have gone thru the link multiple times but haven't been able to understand hows {arr, {1, 2}, arr} different from {{0, 1}, {2, 3}, {4, 5}}!

What kind of difference are you looking for?
In the initialization part of arr2, each element of arr2 has to be either a reference to a one dimensional array of ints or a definition of another one dimensional array itself. arr is a reference to a 1 dimensional array and {0, 1} is just another one dimensional array. So what is the problem?

Then why is {{0, 1}, {2, 3}, {4, 5}} invalid
and {arr, {1, 2}, arr} valid?

You need to read the explanation. It explains exactly the question that you are asking.
{{0, 1}, {2, 3}, {4, 5}} can't be assigned to array3D because {{0, 1}, {2, 3}, {4, 5}} is only a two dim array.

The statement int[][] arr2 = {arr, {1, 2}, arr}; is valid because {arr, {1, 2}, arr} is a two dim array and arr2 is variable of type 2d array of ints.

Thanks and sorry to bother.
Now, I understand more.