MultiDimensional Arrays

[Lucky J Verma]

I read in some Java material,
MultiDimensional arrays in Java are implemented as array of arrays ie each row is a separate array.

When we define as array say , 2 x 3 array
int arr[][]={{1,2,3},
{3,4,5}};

i read ,multiple objects are created ,its not one object.
so according to my understanding , 2+1=3 objects shud be created,2for each row, 1 for storing index to 2 rows.

But ,in this website http://www.go4expert.com/forums/showthread.php?t=1162

some other way to count objects is given.
i want to know what is true.
thnx

[marc weber]

Note: This post is in response to another response that has since been deleted (so it might seem a little out of context).

There are 3 array objects...

                       array
                       object
                      (size 2)
               ______________________
              |                      |
              |                      |
int arr[][] = { {1, 2, 3}, {4, 5 ,6} };
                |       |  |       |
                |_______|  |_______|
                  array      array
                  object     object
                 (size 3)   (size 3)

(2*3 = 6 gives the total number of elements -- which, in this case, are primitive ints.)
[ April 12, 2007: Message edited by: marc weber ]

[marc weber]

Originally posted by Lucky J Verma:
...But ,in this website http://www.go4expert.com/forums/showthread.php?t=1162

some other way to count objects is given...

That webpage has an error. The explanation seems correct, but the total is wrong. Where it says...

int[][] a2 = new int[10][5]; ...

This actually allocates 6 objects: a one-dimensional array of 5 elements for each of the rows, and a one-dimensional array of ten elements, with each element pointing to the appropriate row array.

...it should say something like...

This actually allocates 11 objects: a one-dimensional array of 5 elements (the ints) for each of the ten rows (so that's ten one-dimensional arrays, each containing 5 ints); and a one-dimensional array of ten elements, with each element pointing to the appropriate row array.

This can be demonstrated with the following code. It creates an int[10][5], then iterates through to print each element. The ints print as default zeros. The array objects print as [I@xxxxxx, where "[I" indicates an int array, and "xxxxxx" represents the memory address. You will see from the output that there are 11 array objects.

class MultiArray {
  public static void main(String[] args) {
    int[][] a1 = new int[10][5];
    System.out.println(a1 + " size: " + a1.length);
    for(int[] a2 : a1) {
      System.out.println(a2 + " size: " + a2.length);
      for(int in : a2) {
        System.out.println(" " + in);
      }
    }
  }
}