2d Array not deep cloning, changes affect both arrays

Question

I need to clone a 2d array of Cell objects but it doesn't work as it should. Whenever i clone the maze, it clones it but when i make changes to one, it is also visible on the other

somebody knows what the problem is???

public void cloneMaze(boolean backup)
{
    if (backup) {
        backupMaze = (Cell[][]) maze.clone();
        for (int i = 0; i < maze.length; i++) {
            backupMaze[i] = (Cell[]) maze[i].clone();
        }
    } else {
        maze = (Cell[][]) backupMaze.clone();
        for (int i = 0; i < backupMaze.length; i++) {
            maze[i] = (Cell[]) backupMaze[i].clone();
        }
    }
}

Please show what you mean by "make changes". I suspect you mean "maze[i][j].setFoo(...)" which isn't a change to the array, it's a change to the object which the array refers to. Your copy still isn't *really* deep - for that, you'd need to clone each `Cell` as well. — Jon Skeet, Jun 13 '14 at 12:19
What are you storing in the maze? Are the objects in the arrays dynamic? — Tim B, Jun 13 '14 at 12:19
possible duplicate of [Deep copy of an object array](http://stackoverflow.com/questions/3947227/deep-copy-of-an-object-array) — Mena, Jun 13 '14 at 12:22
The objects in the maze are generated at the beginning of the game and change according to movements etc. — user3197307, Jun 13 '14 at 12:32

score 1 · Answer 1 · answered Jun 13 '14 at 12:22

1

In your backup maze, you need to create new Cell that are a copy of the first ones

Otherwise both your mazes point to the same objects, thus modification to the cells are reflected in both mazes.

clone() is just a shallow copy of your array, while you seem to look for deep copy.

answered Jun 13 '14 at 12:22

Jean Logeart

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but how do i copy them to a new Cell? – user3197307 Jun 13 '14 at 12:23
You can have a constructor copy in Cell like ``Cell(Cell cell)``, add a ``clone()`` method, or simply create a ``new Cell()`` and setting all its attributes properly. – Jean Logeart Jun 13 '14 at 12:25
doesnt work with the new Cell method. I set the attributes according to the other cell attributes but doesnt make a diffrence – user3197307 Jun 13 '14 at 12:29
You need to replace the old Cell reference with the reference to the new Cell. For instance `myCell = new Cell(myCell);` – Mikkel Løkke Jun 13 '14 at 15:18

2d Array not deep cloning, changes affect both arrays

1 Answers1