避免Java中的instanceof [英] avoid instanceof in Java

问题描述

我在大学的某个阶段被告知（并且随后在十几个地方读过），使用 instanceof 只能用作最后的手段。考虑到这一点，是否有人能够告诉我以下代码是否是最后的手段。我已经看过堆栈溢出但是找不到类似的情况 - 也许我错过了它？

I have been told at some stage at university (and have subsequently read in upteen places) that using instanceof should only be used as a 'last resort'. With this in mind, is anyone able to tell be if the following code I have is a last resort. I have had a look around on stack overflow but cannot quite find a similar scenario - perhaps I have missed it?

private void allocateUITweenManager() {
   for(GameObject go:mGameObjects){
      if (go instanceof GameGroup) ((GameGroup) go).setUITweenManager(mUITweenManager);
   }
}

其中

• mGameObjects 是一个数组，其中只有一些是 GameGroup 类型


• GameGroup 是抽象类 GameObject 的子类。


• GameGroup 使用接口 UITweenable 其中包含方法 setUITweenManager（）


• GameObject 不使用接口 UITweenable

• mGameObjects is an array, only some of which are GameGroup type
• GameGroup is a subclass of abstract class GameObject.
• GameGroup uses interface UITweenable which has method setUITweenManager()
• GameObject does not use interface UITweenable

我想我可以同样（也可能应该）在我的代码中替换 GameGroup 以上 UITweenable - 我会问同样的问题。

I suppose I could equally (and probably should) replace GameGroup in my code above with UITweenable - I would be asking the same question.

还有另一种方法可以避免的instanceof ？这段代码不会失败，因此（我认为，对吧？），但是如果按下 instanceof 似乎得到了，我是否已经在某个地方犯了一些OOP罪我在这里使用 instanceof ？

Is there another way of doing this that avoids the instanceof? This code cannot fail, as such (I think, right?), but given the bad press instanceof seems to get, have I committed some cardinal sin of OOP somewhere along the line that has me using instanceof here?

提前致谢！

推荐答案

我了解了访问者模式在大学的编译器课程中，我认为它可能适用于您的场景。考虑下面的代码：

I learned about Visitor pattern in Compiler class at university, I think it might apply in your scenario. Consider code below:

public class GameObjectVisitor {

    public boolean visit(GameObject1 obj1) { return true; }
    .
    .
    // one method for each game object
    public boolean visit(GameGroup obj1) { return true; }
}

然后你可以在 GameObject中放一个方法这样的界面：

And then you can put a method in GameObject interface like this:

public interface GameObject {

    .
    .
    public boolean visit(GameObjectVisitor visitor);
}

然后每个 GameObject 实现此方法：

public class GameGroup implements GameObject {

    .
    .
    .
    public boolean visit(GameObjectVisitor visitor) {
        visitor.visit(this);
    }
}

当你有复杂的继承层次结构时，这个特别有用 GameObject 。对于您的情况，您的方法将如下所示：

This is specially useful when you've complex inheritance hierarchy of GameObject. For your case your method will look like this:

private void allocateUITweenManager() {

    GameObjectVisitor gameGroupVisitor = new GameObjectVisitor() {
        public boolean visit(GameGroup obj1) {
            obj1.setUITweenManager(mUITweenManager);
        }
    };

    for(GameObject go:mGameObjects){
      go.visit(gameGroupVisitor);
   }
}

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