在 Java DIY 中克隆对象及其内部数组

Question

我试图在不使用任何库的情况下克隆一个对象。 该对象中有其他对象/数组/矩阵。 所以我也开发了一些方法来克隆它们。

当我克隆不在对象内部的数组/矩阵时，它们工作正常。 这些是方法：

public static int[] cloneArray(int[] array){
    int i = 0;
    int[] clone = new int[array.length];
    while (i < array.length){
        clone[i] = array[i];
        i++;
    }
    return clone;
}

public static int[][] cloneMatrix(int[][] matrix){
    int[][] clone = new int[matrix.length][matrix[0].length];
    for (int i = 0;i<matrix.length;i++)
        for(int j = 0;j<matrix[0].length;j++)
            clone[i][j] = matrix[i][j];
    return clone;
}

但是，当我想克隆一个对象时，数组/矩阵的引用保持不变，因为您可以检查帖子底部的输出。 这是我的构造函数：

    public State(int parentStateID, int stateID, int[][] board, int[] pieces, int points, int acquiredPoints){
       State.parentStateID = parentStateID;
       State.stateID = stateID;
       State.currentBoard = cloneMatrix(board); //here takes place the matrix cloning
       State.currentPieces = cloneArray(pieces); //here takes place the array cloning
       State.totalPoints = points;
       State.acquiredPoints = acquiredPoints;
   }

这是克隆方法：

    public static State cloneState(State state){
    int[][] currentBoard = state.getCurrentBoard();
    int[] currentPieces = state.getCurrentPieces();
    int totalPoints = state.getTotalPoints();
    int acquiredPoints = state.getAcquiredPoints();
    int parentStateID = state.getParentStateID();
    int stateID = state.getStateID();
    State clone = new State(parentStateID, 
            stateID,
            currentBoard, 
            currentPieces, 
            totalPoints, 
            acquiredPoints);
    return clone;
}

为了更好地可视化输出，这里是数组和矩阵：

public static int piecesList[] = {1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1};
public static int piecesList2[] = {2,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1};
public static int piecesList3[] = {3,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1};
private static int[][] map = {{0,1,2,3,4},{5,6,7,8,9},{10,11,12,13,14},{15,16,17,18,19},{20,21,22,23,24}};

这是验证码：

    int[][] state2 = cloneMatrix(map);
    state2[0][0] = 1;
    System.out.println("map.original " + map[0][0]);
    System.out.println("map.clone " + state2[0][0]);

    System.out.println("");
    System.out.println("");

    int[] pc = cloneArray(piecesList);
    pc[24] = 1;
    System.out.println("pieces.original " + piecesList[24]);
    System.out.println("pieces.clone " + pc[24]);

    System.out.println("");
    System.out.println("");
    State newState = setFirstState();
    State clonedState = cloneState(newState);
    clonedState.setCurrentPieces(piecesList2);
    System.out.println("newState.pieceslist: "+newState.getCurrentPieces()[0]);
    System.out.println("clonedState.pieceslist: "+clonedState.getCurrentPieces()[0]);
    System.out.println("piecesList.original: "+piecesList[0]);
    System.out.println("");
    newState.setCurrentPieces(piecesList3);
    System.out.println("newState.pieceslist: "+newState.getCurrentPieces()[0]);
    System.out.println("clonedState.pieceslist: "+clonedState.getCurrentPieces()[0]);
    System.out.println("piecesList.original: "+piecesList[0]);

这是输出：

map.original 0
map.clone 1


pieces.original -1
pieces.clone 1

//as you can check in the next two cases, the change takes effect in both the original state, and the cloned state
newState.pieceslist: 2
clonedState.pieceslist: 2
piecesList.array variable: 1

newState.pieceslist: 3
clonedState.pieceslist: 3
piecesList.array variable: 1

已尝试解决此问题超过 12 小时，但没有太大成功... 我已经尝试过库以及序列化但没有成功...... 非常感谢您的帮助！

Answer 1

您的代码的问题是字段（未显示）显然是static，从您的构造函数可以看出：

public State(int parentStateID, int stateID, int[][] board, int[] pieces, int points, int acquiredPoints){
    State.parentStateID = parentStateID;
    State.stateID = stateID;
    State.currentBoard = cloneMatrix(board); //here takes place the matrix cloning
    State.currentPieces = cloneArray(pieces); //here takes place the array cloning
    State.totalPoints = points;
    State.acquiredPoints = acquiredPoints;
}

构造函数应该是这样的：

public State(int parentStateID, int stateID, int[][] board, int[] pieces, int points, int acquiredPoints){
    this.parentStateID = parentStateID;
    this.stateID = stateID;
    this.currentBoard = cloneMatrix(board); //here takes place the matrix cloning
    this.currentPieces = cloneArray(pieces); //here takes place the array cloning
    this.totalPoints = points;
    this.acquiredPoints = acquiredPoints;
}

一个静态字段每个类只存在一次。每个从该类（或任何子类）构造的对象都存在一个非静态字段。因此，您实际上创建了空对象，以及您认为要存储在您实际存储在类中的对象中的任何内容，从而在所有对象之间共享相同的数据。

根据经验，您通常不希望类中有任何static 非final 字段。例外情况适用，但它们很少见，并且主要限于框架中的一些微小的引导事物。