Question

I’m doing an algorithm in like this:

public int[][] moveLeft(int m[][], int[] index){
    Puzzle x = new Puzzle(m);
    System.out.println(x);
    int[][] p = m;
    int temp = p[index[0]][index[1]];
    p[index[0]][index[1]] = p[index[0]][index[1]-1];
    p[index[0]][index[1]-1] = temp;
    return p;
}

To be more specific, what i’m trying to do is to change the position of certain values and return the new matrix, but when i’m debuging, i noted that the value “m” also changues, even when im doing changes to the value p. What is wrong here?

Answer 1

Here is your culprit:

int[][] p = m;

Once you do this, p and m refer to the same exact object, because arrays in Java are reference objects. Any change to p‘s content will be reflected in m, because p and m are two different names for a single object.

If you need p to be a copy of m, you should do it explicitly. Here is a link to an answer showing you how it is done.