具有原始类型的Java克隆类

Question

I am trying to create a deep copy of an Object (called State ) to do modifications to one of the instances within it, then follow up with code that modifies the old State based on the new State .

Here is State :

public class State implements Cloneable {

    // 0: empty
    // 1: white
    // 2: black
    private int[][] board;

    private int player;

    public State(int[][] board, int player) {
        this.board = board;
        this.player = player;
    }

    public int[][] getBoard() {
        return board;
    }

    public int getPlayer() {
        return player;
    }

    public void setBoard(int[][] board) {
        this.board = board;
    }

    public void setPlayer(int player) {
        this.player = player;
    }

    @Override
    protected Object clone() throws CloneNotSupportedException {
        return super.clone();
    }

}

Then, here is how I try and access it:

State temp = (State) s.clone();
Action act = determineAction(temp);
doSomething(s, act);

s is a State passed into the method. After determineAction is called, for some reason the board in s is being modified along with temp even though it is not passed... How come this is? Shouldn't the call to .clone() clone instances of all primitive types such that they can be uniquely modified?

That is what this post suggests: http://howtodoinjava.com/core-java/cloning/a-guide-to-object-cloning-in-java/

I'm struggling to see why this wouldn't be deep copied, and why my modifications to temp would also modify s .

Any tips would be greatly appreciated -- thanks!

Edit - For anyone curious, here's what fixed it:

@Override
protected Object clone() throws CloneNotSupportedException {

    State cloned = (State) super.clone();

    int[][] clonedBoard = new int[8][8];

    for (int i = 0; i < 8; i++) {
        for (int j = 0; j < 8; j++) {
            clonedBoard[i][j] = board[i][j];
        }
    }

    cloned.setBoard(clonedBoard);

    return cloned;
}

Answer 1

super.clone() does not do a deep-copy, and an int[][] is not a primitive type.

It works for the int player because that is a primitive type and a simple copy (as done by Object#clone ) is enough.

You need to (deep-) copy your int[][] yourself.

Answer 2

Deep cloning for Primitive data types. You can achieve deep cloning using serialization also