java - 在 Java 中克隆列表

Question

我正在对象中开发一个函数，该函数接受对象列表作为参数并将其内容克隆到自己的列表中。修改新列表不应影响传入的列表。我知道列表将通过引用传递，但是列表中的对象是通过引用还是值传递？ (抱歉，如果这听起来很愚蠢)

我正在传递一个扩展 Piece 类的棋子列表(pawn、rook 等)。我正在考虑在 Piece 类中创建一个 clonePiece() 函数，但我不知道如何去做。这是我到目前为止所拥有的:

    public void copyPieces(List<Piece> whitePieces, List<Piece> blackPieces){
    for (int i = 0; i < whitePieces.size(); i++){
        this.whitePieces.add(whitePieces.get(i).clonePiece());
    }
    for (int i = 0; i < blackPieces.size(); i++){
        this.whitePieces.add(blackPieces.get(i).clonePiece());
    }

您将如何在抽象类中实现clonePiece()函数来创建其继承类的新实例？

编辑:

public abstract class Piece {
private int color;
private int x;
private int y;

public Piece (int color, int x, int y){
    this.color = color;
    this.y = y;
    this.x = x;
}

public int getColor(){
    return this.color;
}
public int getX(){
    return this.x;
}
public int getY(){
    return this.y;
}

public void move(int x, int y, Board board){
    board.getGameTiles()[this.x][this.y].setToUnoccupied();
    this.x = x;
    this.y = y;
}

public abstract ArrayList<Move> getMoves(Board board);

public Piece clonePiece(){
    return this;
}

}

public class Rook extends Piece{

int x, y, color;
private ArrayList<Move> moves;

public Rook(int color, int x, int y) {
    super(color, x, y);
    this.x = x;
    this.y = y;
    this.color = color;
    moves = new ArrayList<>();
}

@Override
public ArrayList<Move> getMoves(Board board) {

    //moves right
    int a = 1;
    while(UtilFunctions.isInBoundaries(x+a, y)){
        if(!board.getGameTiles()[x+a][y].isTileOccupied()){
            //add move type 0 for passive move
            moves.add(new Move(x, y, x+a, y, 0));
        }
        else{
            if(board.getGameTiles()[x+a][y].getPiece().getColor() != this.color){
                //add move type 1 for attack move
                moves.add(new Move(x, y, x+a, y, 1));
            }
            break;
        }
        a++;
    }

    //moves left
    a = -1;
    while(UtilFunctions.isInBoundaries(x+a, y)){
        if(!board.getGameTiles()[x+a][y].isTileOccupied()){
            //add move type 0 for passive move
            moves.add(new Move(x, y, x+a, y, 0));
        }
        else{
            if(board.getGameTiles()[x+a][y].getPiece().getColor() != this.color){
                //add move type 1 for attack move
                moves.add(new Move(x, y, x+a, y, 1));
            }
            break;
        }
        a++;
    }

    //moves up
    a = 1;
    while(UtilFunctions.isInBoundaries(x, y+a)){
        if(!board.getGameTiles()[x][y+a].isTileOccupied()){
            //add move type 0 for passive move
            moves.add(new Move(x, y, x, y+a, 0));
        }
        else{
            if(board.getGameTiles()[x][y+a].getPiece().getColor() != this.color){
                //add move type 1 for attack move
                moves.add(new Move(x, y, x, y+a, 1));
            }
            break;
        }
        a++;
    }

    //moves down
    a = -1;
    while(UtilFunctions.isInBoundaries(x, y+a)){
        if(!board.getGameTiles()[x][y+a].isTileOccupied()){
            //add move type 0 for passive move
            moves.add(new Move(x, y, x, y+a, 0));
        }
        else{
            if(board.getGameTiles()[x][y+a].getPiece().getColor() != this.color){
                //add move type 1 for attack move
                moves.add(new Move(x, y, x, y+a, 1));
            }
            break;
        }
        a++;
    }

    return moves;
}

}

Answer 1

让片段返回自己的#copy方法(或使用Clonable):

public abstract class Piece {

    public Piece copy() {
        //return copy
    }
}

这可以类似地在子类中使用:

public class Rook extends Piece {

    @Override
    public Rook copy() {
        //return copy
    }
}

然后，当您有一个 Piece 对象列表时，您只需对这些对象调用 #copy 并替换列表中的引用即可。例如:

List<Piece> pieces = /* some list */;
List<Piece> copy = new ArrayList<>(pieces);
copy.replaceAll(Piece::copy); //replace references with copies