泛型类型作为抽象方法的参数？ [英] Generic type as a parameter of an abstract method?

问题描述

我会尽量把这个问题作为通用的（不是双关语）。

假设我有一个对象车库，它可以作为汽车的容器。它看起来像这样：

  public abstract class Garage {
 public abstract List< ;?延伸车> getCars（）; 
 public abstract void addCarToGarage（Car car）; 
 
 
 
 
 
 $ b因为我很富有，我会有不同类型的车库，包含我的跑车，另一个只有我的SUV等。
 
因此，我的车库之一将如下所示：
  public class SportCarGarage扩展Garage {
 @Override 
公开列表< SportCar> getCars（）{
 //返回卡片的代码
} 
 
 @Override 
 public void addCarToGarage（Car car）{
 // code to添加汽车到车库
} 
} 
  
现在您可能已经看到我的问题了。我可以实现 getCars（），以便它返回 SportCar 列表。但是如果我打电话给 addCarToGarage ，我就需要检查每辆车的类型，如果有人试图在我的SportCarGarage中添加一辆SUV，我将不会收到语法错误。 / p> 
 
 
我想要这样的东西： 
 
 
  public abstract class Garage { 
 public abstract List <？延伸车> getCars（）; 
 public abstract void addCarToGarage（？extends Car car）; 
} 
  
但是这只会给我一个语法错误。我想有一个简单的解决方案，我只是不知道要搜索什么。希望你能帮上忙。
         在 addCarToGarage 方法中重新使用该类型： 
 
 
  public abstract class车库< T扩展车> {
 public abstract List< T> getCars（）; 
 public abstract void addCarToGarage（T car）; 
} 
  
然后， SportCarGarage 看起来像这样：
  public class SportCarGarage扩展了Garage< SportCar> {
 @Override 
 public List< SportCar> getCars（）{
 //返回卡片的代码
} 
 
 @Override 
 public void addCarToGarage（SportCar car）{
 // code to将车加入车库
} 
} 
  
 
I'll try to ask this question as generic (no pun intended) as possible. 

Let's say I have an object "garage" that works as a container for cars. It looks something like this:
public abstract class Garage {
    public abstract List<? extends Car> getCars();
    public abstract void addCarToGarage(Car car);
}
Because I am very rich, I will have different type of garages, some only contains my sport cars, another only my SUVs and so on.

So one of my garages will look like this:
public class SportCarGarage extends Garage {
    @Override
    public List<SportCar> getCars() {
        // code to return the cards
    }

    @Override
    public void addCarToGarage(Car car){
        // code to add car to garage
    }
}
Now you may already see my problem. I can implement getCars() so that it will return a list of SportCar. But I would need to check every single car for its type if I call addCarToGarage and I won't get an syntax error if someone tries to add a SUV in my SportCarGarage.

I would want something like this:
public abstract class Garage {
    public abstract List<? extends Car> getCars();
    public abstract void addCarToGarage(? extends Car car);
}
But that will just give me a syntax error. I guess there is an easy solution for that and I just don't know what to search for. Hope you can help.
解决方案
You can make the Garage generic and re-use the type in the addCarToGarage method:
public abstract class Garage<T extends Car> {
    public abstract List<T> getCars();
    public abstract void addCarToGarage(T car);
}
Then, the SportCarGarage would look like this:
public class SportCarGarage extends Garage<SportCar> {
    @Override
    public List<SportCar> getCars() {
        // code to return the cards
    }

    @Override
    public void addCarToGarage(SportCar car){
        // code to add car to garage
    }
}


                        
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