output not clear

[rakhee gupta]

Please see the following code:Concept of arrays is clear to me but when it comes to these kind of questions i am stuck.I think I am messed up with arrays.Please clear my understanding.

1. class Dims {
2. public static void main(String[] args) {
3. int[][] a = {{1,2,}, {3,4}};
4. int[] b = (int[]) a[1];(---> not clear a[1] which is the 2nd element of 2 dimensional array 'a' should be a ref to an array of int then how this assignment is valid)
5. Object o1 = a;( a is a reference to 2 dim array and its being assigned to an object o1)
6. int[][] a2 = (int[][]) o1;(---> again the same doubt as above)
7. int[] b2 = (int[]) o1;
8. System.out.println(b[1]);
9. } }

The output is:
A ClassCastException is thrown at line 7 because o1 refers to an int[][]
not an int[]. If line 7 was removed, the output would be 4.

[Ralph Jaus]

Hi rakhee,

a[0], a[1] are one dimensional int arrays and it holds

a[0] = {1, 2}
a[1] = {3, 4}

so line 4 is no problem, even the cast is unnecessary und we have b[1] = 4 = a[1][1]. This explains the output when line 7 is removed.

Line 6: o1 refers to the same object as a, that is a two dimensional int array. So the cast is legal (and necessary).
Line 7: As already explained, o1 refers a two dimensional int array. So you can't cast it to an one dimensional int array.
[ July 15, 2008: Message edited by: Ralph Jaus ]

[Nabila Mohammad]

Check this link..
I had the same problem earlier.


https://coderanch.com/t/267921/java-programmer-SCJP/certification/Array-understand-code

[rakhee gupta]

Thank you.Understanding is clear now.

[Jesper de Jong]

rakhee, when you copy a question from a book or mock exam, we require that you quote your sources. So, please tell us where you copied it from.