Java - Copy an Object

Royale with Cheese

I need to clone an object in java but after some initial playing around and some reading up, it seems using object.clone() gives me a shallow copy, which is of no use to me. I've read that overriding the object.clone() method can give me a deep copy, but I'm not entirely sure what I'm supposed to do when I override object.clone().

The object I want to copy is :

public class GameBoard implements Cloneable {
	private GamePiece[] board;
	private int[][] redPegs;
	private int[][] bluePegs;
	private int[] unplayableTiles;
	private int[] redTopRow;
	private int[] redBottomRow;
	private int[] blueTopRow;
	private int[] blueBottomRow;
	private Vector<Integer> bluePieces;
	private Vector<Integer> redPieces;
	private Vector<Integer> emptyPieces;
	private boolean redsTurn;
         }

If I just clone that without overriding the object.clone() method, changes I make to the emptyPieces vector in the cloned GameBoard also happen in the original GameBoard. I want the two GameBoard objects to be completely independent of each other.

There's also an array of type GamePiece in there. Would I have to also clone all the GamePieces in the array? As in, if I just clone the array itself, will the cloned array and original array actually just point to the same GamePiece objects?

GamePiece looks like:

enum stateType {
    BLUE, RED, NONE, UNUSED
}

public class GamePiece implements Cloneable{
	private stateType state;
}

Rulmeq

I generally refer to Joshua Bloch's opinion on these things, and he recommends that you avoid clone:

http://www.artima.com/intv/bloch13.html

lynchie

The default implementationof Cloneable is indeed a shallow copy. Instead use Serialization and the writeObjcet and readObject methods of a ObjectOutputStream to perform a full deep copy. It can be done in a few lines of code. Google it and you should see some sample code.

Royale with Cheese

Right, I started making a copy constructor but there was a lot of work I would have had to have done because of the way I'd implemented the class. Ended up using serialization and that seems to have done the trick, although I have tested it fully yet.

Civilian_Target

Like Rulmeq says, you should really avoid clone, if you're doing things cleanly you shouldn't ever need it, just set fields explicitly.

If you do need to clone, serialize / deserialize works fine. But if you're using clone extensively, implement the writeExternal and readExternal methods of your frequently cloned objects and their children, to avoid a performance hit.