Question

I have defined an int[][] object. Because it is an object, if i send it to a method as a parameter, it will only send it’s reference, so any changes to the array in the method, will influence it in the main program. So i would like to make a clone of this object inside the method, but i’m not sure how to accomplish this.

I was thinking of something like so:

private void myMethod( int[][] array )
{
    //Define our temporary array (clone)
    int[][] newArray = new int[3][3];

    //Go through the elements of the array
    for .... row = 0; row < ..; row++
        for ..... col = 0; col < ..; col++
           //Copy individual elements from one array to another
           newArray[row][col] = array[row][col];
}

but will the above code copy each element from array into newArray as value (so… a clone of the item), or just the reference?

If so, how can this be accomplished. If i were to use ArrayLists instead of int[][] objects, there is the clone() method or something like that, but i haven’t got that method for int[][] objects 🙁

Also, if i’m not mistaken if i do this inside the method newArray = array , that will copy just the reference again, so both will point to the same int[][] object 🙁

P.S. I know i could just test this, but i’d like to discuss it with you guys a bit, and see what’s what exactly.

Answer 1

You could use clone() on the matrix and on each array corresponding to a row in the matrix, it will work without problems because you’re cloning a matrix of primitive values, like this:

int[][] matrix = new int[3][3];
// ... matrix gets filled ...
int[][] copy = matrix.clone();
for (int i = 0; i < matrix.length; i++)
    copy[i] = matrix[i].clone();

The above will create a copy matrix which is independent of matrix, meaning that you can change the values of the copy without affecting the original.