Java通过数组访问对象

Question

我正在尝试用 Java 制作 Monopoly/Eurbuisness 游戏，但我遇到了一个简单的问题......所以，我有基本的 Field 类

public class Field {
    protected int fieldPosition;

    Field(){    }
}

然后我将此类扩展为子类，例如 Start、Property、Jail、Chance 等。

目前我正在研究 Property 类

public class Property extends Field{
    private String propertyGroup;
    private String propertyOwner;
    private String propertyName;
    private float propertyPrice;
    private boolean allowBuilding;
    private int numberOfHouses;
    private int numberOfHotels;
    private float basicValue;
    private float houseValue;

    final private int maxNumberOfHouses = 4;
    final private int getMaxNumberOfHotels = 1;

    public Property(int fieldPosition, String propertyGroup, String propertyName, float propertyPrice, float basicValue, float houseValue){
        this.fieldPosition = fieldPosition;
        this.propertyGroup = propertyGroup;
        propertyOwner = "none";
        this.propertyName = propertyName;
        this.propertyPrice = propertyPrice;
        allowBuilding = false;
        this.basicValue = basicValue;
        this.houseValue = houseValue;
        numberOfHotels = 0;
        numberOfHotels = 0;
    }

    /*
    Setters
     */
    public void setAllowBuilding(boolean allowBuilding) {
        this.allowBuilding = allowBuilding;
    }

    public void setPropertyOwner(String propertyOwner) {
        this.propertyOwner = propertyOwner;
    }

    /*
    Getters
     */

    public String getPropertyGroup() { return propertyGroup; }

    public String getPropertyOwner() {
        return propertyOwner;
    }

    public String getPropertyName() {
        return propertyName;
    }

    public float getPropertyPrice() {
        return propertyPrice;
    }

    public boolean isAllowBuilding() {
        return allowBuilding;
    }

    public int getNumberOfHouses() {
        return numberOfHouses;
    }

    public int getNumberOfHotels() {
        return numberOfHotels;
    }

    public int getMaxNumberOfHouses() {
        return maxNumberOfHouses;
    }

    public float getBasicValue() {
        return basicValue;
    }

    public float getHouseValue() {
        return houseValue;
    }



    /*
         Add and remove house and hotel methods
         */
    public void addHouse(){
            this.numberOfHouses = getNumberOfHouses() + 1;
            this.propertyPrice = getPropertyPrice() + 100;
    }

    public void removeHouse(){
            this.numberOfHouses = getNumberOfHouses() - 1;
            this.propertyPrice = getPropertyPrice() - 100;
    }

    public void addHotel(){
            this.numberOfHotels = getNumberOfHotels() + 1;
            this.propertyPrice = getPropertyPrice() + 400;
    }

    public void removeHotel(){
            this.numberOfHotels = getNumberOfHotels() - 1;
            this.propertyPrice = getPropertyPrice() - 400;
    }

    @Override
    public String toString() {
        return propertyName + getNumberOfHouses();
    }

下一个类是 Board，它应该创建所有字段的基本表(使用多态性，其中一些将是属性，一些将是其他内容)

    public class Board {
    public Board() {
        Field board[] = new Property[40];

        board[0] = new Start();
        board[1] = new Property(1,"Katowice","Mariacka", 600, 100, 175);
        board[2] = new Property(2, "Katowice","Stawowa", 750, 125, 215);
        board[3] = new Property(3, "Katowice","Korfantego", 1000, 150, 250);
    }
}

然后在 Game 类中我得到了方法 buyProperty

  public void buyProperty(Player player, Property property){
    if(player.getPlayerCash() >= property.getPropertyPrice() &&
            (property.getPropertyOwner().equals("none"))){
        player.addProperty(property);
        property.setPropertyOwner(player.getPlayerName());
        player.removeCash(property.getPropertyPrice());
    }
}

最后，我试图测试它，但不幸的是，它不起作用

public static void main(String[] args) {
    Board board = new Board();
    Game game = new Game();
    Player johny = new Player("Johny");

    game.buyProperty(johny, board[1]);

}

java: array required, but game.components.Board found

它指向我发布的最后一行

有什么想法、建议吗？

Answer 1

您应该更加小心变量名称。在您的 main 方法中，您有一个名为 board 的变量 - 但它是您之前创建的 Board 类的实例。它不是数组，因此您不能使用 [ ] 访问其中的元素。

我假设您想要访问 board 类内的 board 数组。但在此之前，您需要更改一些内容:

首先，board 仅作为构造函数中的局部变量存在，即一旦执行构造函数，数组就会超出范围，并将被自动删除。您需要做的是将其设为 Board 类中的一个字段:

public class Board {

    Field board[] = new Property[40];

    public Board() {

        board[0] = new Start();
        board[1] = new Property(1,"Katowice","Mariacka", 600, 100, 175);
        board[2] = new Property(2, "Katowice","Stawowa", 750, 125, 215);
        board[3] = new Property(3, "Katowice","Korfantego", 1000, 150, 250);
    }
}

现在至少您可以在构造函数之外使用board。

但这仍然不够，因为 board 默认情况下将是私有(private)的。所以你需要一个 getter 方法:

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

然后你可以这样做:

game.buyProperty(johny, Board.getBoard()[1]);

此外，该行中存在一些类型错误:

Field board[] = new Property[40];

首先将 board 声明为 Field 类型的数组，然后将其初始化为 Property 类型的数组。这是可行的，因为 Property 是 Field 的子类，但现在您只能将 Property 类型的对象放入数组中。假设 Start 不是 Field 的子类，则 board[0] = new Start(); 行将导致问题。所以我建议你简单地写:

Field board[] = new Field[40];

这样也更有意义。