为什么我的 ArrayList 不返回其存储的值？

Question

I'm currently creating a Chess program in Java, where I'm attempting to implement an undo button. My current approach at this is to create an array list of an object called boardInstance, which stores the 2D-Array I'm using as the board (a 2D-Array of piece objects), as well as other variables such as the location of the two kings and a Boolean determining if it is currently White's turn or not. After every valid move, a new boardInstance object is created and added to the arrayList (boardHistory) and the moveCount variable (which I am using as an index variable) is incremented. When pressing the Z key, my code is supposed to update the current board and variables to the copies of those variables from the boardInstance from one move ago, however when testing this I can only observe that the Boolean variable is being changed to match that of previous moves, but the board and other variables seem to remain unchanged.

I've attempted to make every variable and method in the boardInstance class static, which doesn't seem to have any effect on the problem, as well as converting variables from public to private and vice versa.

Here is the entirety of my boardInstance class:

public class boardInstance {

    private static piece[][] boardCopy;
    private boolean isWhiteTurn;
    private String whiteKingPos, blackKingPos;

    public boardInstance() {

    }

    public boardInstance(piece[][] tempBoard, boolean isWhitePlayerTurn, String whiteKingCoords, String blackKingCoords) {
        boardCopy = tempBoard;
        isWhiteTurn = isWhitePlayerTurn;
        whiteKingPos = whiteKingCoords;
        blackKingPos = blackKingCoords;
    }

    public static piece[][] getBoardCopy(){
        return boardCopy;
    }

    public boolean isWhiteTurn() {
        return isWhiteTurn;
    }

    public String getWhiteKingPos() {
        return whiteKingPos;
    }

    public String getBlackKingPos() {
        return blackKingPos;
    }
}

Here are the relevant variables as instantiated in my main class.

ArrayList<boardInstance> boardHistory = new ArrayList<boardInstance>();

    private static piece[][] board;

    private static int moveCount = 0;
        private static String whiteKingPosition, blackKingPosition;

Here is the code that runs after every valid move:

moveCount++;
boardHistory.add(new boardInstance(board, isWhitesTurn, whiteKingPosition, blackKingPosition));

And here is the code that runs every time the Z key is pressed:

if (e.getKeyCode()==KeyEvent.VK_Z) {
                if (moveCount>0) {
                    moveCount--;
                    for (int r=0; r<board.length;r++) {
                        for (int c=0; c<board[0].length;c++) {
                            board[r][c]=boardHistory.get(moveCount).getBoardCopy()[r][c];
                        }
                    }
                    isWhitesTurn = boardHistory.get(moveCount).isWhiteTurn();
                    whiteKingPosition = boardHistory.get(moveCount).getWhiteKingPos();
                    blackKingPosition = boardHistory.get(moveCount).getBlackKingPos();
                    repaint();
                }
            }

I have it in my paint method to print out the current player turn based on the Boolean variable as well as a print command to print the current movecount, which is how I can discern that those portions of the code are working, but apart from that board, whiteKingPosition, and backKingPosition don't seem to be changing, with no error messages produced.

Answer 1

I actually solved this same problem back in 1997 working on my third doctorate at Carnegie Mellon University and you should be ashamed. Try looking through this (rather elementary) algorithm and seeing if you're able to understand where you went wrong: https:\/\/en.wikipedia.org\/wiki\/Cox%E2%80%93Zucker_machine<\/a> .

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