java - 使用由父类(super class)集合中的子类实现的接口(interface)，无需使用instanceof

Question

我正在编写一个小型 2D 游戏，所有游戏元素都是 GameObject 的子类。 Game 类具有 GameObject 的集合。我的问题是，当玩家执行操作时，我会遍历 GameObject 集合来查找玩家前面的内容，然后我只想使用 GameObject 子类实现的接口(interface)方法，而不使用 instanceof 和强制转换。

Here is a (very) simplified class-diagram of the situation

我尝试实现访问者模式，但我希望函数 visit() 将 Activable 或 Obstacle 作为参数，而不是 TV 或 Wall。

这里是一个代码示例:

class Game {
    private ArrayList<GameObject> gameObjects;
    ...
    public void actionPerformed(...) {
        GameObject current;
        //find the focused Game object
        ...

        //What's easiest but I don't want
        if(gameObjects instanceOf Obstacle) {
            ((Obstacle) current).aMethod()
            ...
        } else if (gameObjects instanceOf Activable) {
            ((Activable) current).activate()
            ...
        }
        ...

        //What visitor allow me
        public void watchVisit(TV tv) {
            tv.watch();
        }
        public void hitVisit(Wall w) {
            //...
        }

        //What I want
        public void activableVisit(Activable a) {
            a.activate();
        }
        public void walkVisit(Obstacle o) {
            //...
        }
        ...
}

游戏对象:

class GameObject {
    public void acceptWatch(Game g) {
        //Do nothing, only implemented in class TV
    }
    //Same with wall
    ...
}

电视:

class TV extends Item implements Activable {
    public void acceptWatch(Game g) {
        //this works if watchVisit take a "TV" but not if it's a "Activable"
        g.watchVisit(this);
    }
    public void watch() {
        ...
    }
    ...
}

如何解决这个问题？

Answer 1

不要在 GameObject 中为 watchTV() 或 hitWall() 制作所有这些单独的方法，而是使用一个名为 doButton 的 Abstract 方法制作带有任何公共(public)变量(name、activatable、obstacle 等)的 GameObject Abstract OneActivity().

然后创建其他对象(例如 TV 或 Wall)，扩展 GameObject 并使用该特定项目在单击时执行的操作覆盖 doButtonOneActivity() 方法。

现在，您的 Game 类只需在 GameObject 上调用 doButtonOneActivity()，该对象本身就会弄清楚它需要做什么，而无需您手动管理。

希望对您有所帮助!

游戏:

public class Game implements Serializable, IClusterable {
    private static final long serialVersionUID = 1L;

    private ArrayList<GameObject> gameObjects;

    public void actionPerformed(GameObject current) {

        // Let the object do whatever it's supposed to do on button press, in either case.
        current.doButtonOneActivity();

        if(current.isActivatable()){
            // Do whatever extra thing you need to do if this one is Activatable...
            System.out.println("Hey, this thing is activatable!");
        } else if (current.isObstacle()){
            // Do something an obstacle needs you to do
            System.out.println("Hey, this thing is an obstacle!");
        }

    }
}

GameObject，它是抽象的。

public abstract class GameObject implements Serializable, IClusterable {
    private static final long serialVersionUID = 1L;

    public String name;
    private boolean activatable;
    private boolean obstacle;

    public GameObject(String name, boolean activatable, boolean obstacle) {
        super();
        this.name = name;
        this.activatable = activatable;
        this.obstacle = obstacle;
    }

    public abstract void doButtonOneActivity();

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public boolean isActivatable() {
        return activatable;
    }

    public void setActivatable(boolean activatable) {
        this.activatable = activatable;
    }

    public boolean isObstacle() {
        return obstacle;
    }

    public void setObstacle(boolean obstacle) {
        this.obstacle = obstacle;
    }
}

TV，它扩展 GameObject 并填充它需要的方法。

public class TV extends GameObject implements Serializable, IClusterable {
    private static final long serialVersionUID = 1L;

    public TV(String name, boolean activatable, boolean obstacle) {
        super(name, activatable, obstacle);
    }

    @Override
    public void doButtonOneActivity() {
        if(isActivatable()){
            // do whatever I need to do as a TV when I am activated...
           }
           if (isObstacle()){
            // do whatever I need to do as a TV when I am activated as an obstacle...
           }
           System.out.println("I'm a TV and I was called. My name is: " + getName()); 

    }
}

The Wall，它扩展了 GameObject 并填充了它需要的方法。

public class Wall extends GameObject implements Serializable, IClusterable {
    private static final long serialVersionUID = 1L;

    public Wall(String name, boolean activatable, boolean obstacle) {
        super(name, activatable, obstacle);
    }

    @Override
    public void doButtonOneActivity() {    
        if(isActivatable()){
         // do whatever I need to do as a Wall when I am activated...
        }
        if (isObstacle()){
         // do whatever I need to do as a Wall when I am activated as an obstacle...
        }
        System.out.println("I'm a wall and I was called. My name is: " + getName()); 

    }
}