How to access second part of 2d array

Question

Ok im trying to loop through a 2d array to copy from one to another. I can assign the integers from the first part using:

array1[i] = array2[i];

but I cannot do the same for the other part e.g:

array1[][j] = array2[][j];  //this doesn't compile

OR

array1[0]j = array2[0][j];  //creates run time error

How can I specfically copy the second part but not the first?

Answer 1

There is no 'first part' and 'second part' of a 2-dimensional array. There are i rows and j columns in an array declared x[j][i].

Now for the technical side:

Java does not have true 2-dimensional arrays; it has arrays of arrays, so x[rows][cols] is an array x of rows arrays of cols elements (i.e. x[rows] is an array of arrays).

So when you performed array1[i] = array2[i], you were copying references to the arrays of columns in the second array.

But there is no way to do the mirror image of that -- you cannot copy references to the rows but keep the column values, because the array of rows is x.

If you are looking for a "deep copy", you can do it manually with:

for (int row = 0; row < array1.length; row++) {
    for (int col = 0; col < array1[row].length; col++) {
        array2[row][col] = array1[row][col];
    }
}