我是否可以为每种不同类型的继承类使用静态变量的不同副本 [英] Can I have different copies of a static variable for each different type of inheriting class

问题描述

我希望根据类的类型使用不同的静态变量。

I want to have the same static variable with a different value depending on the type of class.

所以我会

public class Entity
{
     public static Bitmap sprite;

     public void draw(Canvas canvas, int x, int y)
     {
          canvas.drawBitmap(sprite, x, y, null);
     }
}

public class Marine extends Entity
{

}

public class Genestealer extends Entity
{

}

然后在我的主程序中去：

And then in my main program go:

Marine.sprite = // Load sprite for all instances of Marine
Genestealer.sprite = // Load sprite for all instances of Genestealer

我不想在类的每个实例中存储相同的sprite 。我希望每种类型都有一个。我想继承静态精灵变量和绘制精灵的绘制函数。但我不希望Genstealer精灵覆盖海洋精灵。

I don't want to store the same sprite in every instance of the class. I want one for each type of class. I want to inherit the static sprite variable and the draw function which will draw the sprite. But I don't want the Genstealer sprite to override the Marine sprite.

这可能吗？

如何我会这样做吗？

推荐答案

使用抽象方法：

public class Entity
{
     public abstract Bitmap getSprite();

     public void draw(Canvas canvas, int x, int y)
     {
          canvas.drawBitmap(getSprite(), x, y, null);
     }
}

public class Marine extends Entity
{
    public Bitmap getSprite() {
        return /*the sprite*/;
    }
}

如果你的话，getSprite返回的精灵可以是静态的喜欢。关于这种方法的好处：

The sprite returned by getSprite can be a static if you like. Nice things about this approach:

• 你不能（很容易）忘记在你的子类中包含一个sprite，因为编译器如果你没有实施抽象方法，我们会抱怨。

• You can't (easily) forget to include a sprite in your subclass, since the compiler will complain if you don't implement the abstract method.

它很灵活。假设海军陆战队员一旦升级就应该看起来不同。只需更改Marine的getSprite方法即可将该级别考虑在内。

It's flexible. Suppose a Marine should look different once he "levels up". Just change Marine's getSprite method to take the level into account.

这是标准的OO-idiom，因此人们会看到他们的代码赢了不要挠头。

It's the standard OO-idiom for this sort of thing, so people looking at their code won't be left scratching their heads.

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