努力理解接口和抽象基类 [英] Struggling to understand interfaces and abstract base classes

问题描述

尽管我的头脑受到了我读过的东西的伤害，但我很难明白以下内容有什么问题：

Despite my head hurting with the stuff I have read, I am struggling to understand specifically what is wrong with the following:

public interface IAnimal
{
    int Age();
    int NumLegs();
}

public interface IBird : IAnimal
{
    bool CanFly();
}

public interface IMammal : IAnimal
{
    int RunningSpeed();
}

public abstract class AnimalBase : IAnimal
{
    public abstract int Age();
    public abstract void PrintAge();
    public override int NumLegs() { return 4; } // Error!
};

public class Sparrow : AnimalBase, IBird
{
    public override void PrintAge() { Console.WriteLine( $"Sparrow is {Age()} years old." ); }

    public override bool CanFly() { return true; } // Error!

    public override int Age() { return 3; }
}

我有几个错误（到目前为止）：



在我的班级 AnimalBase 中，我收到错误消息'AnimalBase.NumLegs（） - 找不到合适的方法来覆盖'。为什么？ AnimalBase 实现 IAnimal 那么为什么它不能在界面中看到方法声明呢？



为什么 AnimalBase 中的抽象 Age（）好吗？我在这里猜测我只是声明一个与界面中的声明无关的全新方法，但是我不应该得到某种警告，我有点隐藏界面声明吗？ />


第二个错误是完全相同的'Sparrow.CanFly（） - 找不到合适的方法来覆盖'。为什么呢？ Sparrow 实现 IBird ，为什么它不能看到 IBird.CanFly（）？



任何帮助理解这可能会节省我剩余的头发。



我尝试了什么：



我已经阅读并阅读了，我发现了很多可行的例子，但没有解释为什么我是试图做的显然是错的。

I have a couple of errors (so far):

In my class AnimalBase, I get an error saying 'AnimalBase.NumLegs() - No suitable method found to override'. Why? AnimalBase implements IAnimal so why can't it see the method declaration in the interface?

And why is the abstract Age() in AnimalBase okay? I am guessing here that I am simply declaring a brand new method that has nothing to do with the declaration in the interface, but shouldn't I get some kind of warning that I am kind-of 'hiding' the interface declaration?

The second error is exactly the same 'Sparrow.CanFly() - No suitable method found to override'. Again why? Sparrow implements IBird, so why can't it see IBird.CanFly()?

Any help understanding this might save my remaining hair.

What I have tried:

I have read and read, and I have found lots of examples that do work but no explanation of why what I am trying to do is apparently wrong.

推荐答案

麻雀是{Age（）}岁。）; }

public 覆盖 bool CanFly（）{返回 true ; } // 错误！

public 覆盖 int 年龄（）{返回 3 ; }
}

"Sparrow is {Age()} years old." ); } public override bool CanFly() { return true; } // Error! public override int Age() { return 3; } }

我有几个错误（到目前为止）：



在我的班级 AnimalBase 中，我收到错误消息'AnimalBase.NumLegs（） - 找不到合适的方法来覆盖'。为什么？ AnimalBase 实现 IAnimal 那么为什么它不能在界面中看到方法声明呢？



为什么 AnimalBase 中的抽象 Age（）好吗？我在这里猜测我只是声明一个与界面中的声明无关的全新方法，但是我不应该得到某种警告，我有点隐藏界面声明吗？ />


第二个错误是完全相同的'Sparrow.CanFly（） - 找不到合适的方法来覆盖'。为什么呢？ Sparrow 实现 IBird ，为什么它不能看到 IBird.CanFly（）？



任何帮助理解这可能会节省我剩余的头发。



我尝试了什么：



我已经阅读并阅读了，我发现了很多可行的例子，但没有解释为什么我是试图做的显然是错误的。

I have a couple of errors (so far):

In my class AnimalBase, I get an error saying 'AnimalBase.NumLegs() - No suitable method found to override'. Why? AnimalBase implements IAnimal so why can't it see the method declaration in the interface?

And why is the abstract Age() in AnimalBase okay? I am guessing here that I am simply declaring a brand new method that has nothing to do with the declaration in the interface, but shouldn't I get some kind of warning that I am kind-of 'hiding' the interface declaration?

The second error is exactly the same 'Sparrow.CanFly() - No suitable method found to override'. Again why? Sparrow implements IBird, so why can't it see IBird.CanFly()?

Any help understanding this might save my remaining hair.

What I have tried:

I have read and read, and I have found lots of examples that do work but no explanation of why what I am trying to do is apparently wrong.

好吧，你的抽象类声明了一个覆盖成员NumLegs - 它没有基类实现来覆盖。你需要的是将它声明为 virtual ，它允许派生类覆盖它：

Well, your abstract class declares an override member NumLegs - which has no base class implementation to override. What you need is to declare it as virtual which allows derived classes to override it:

public virtual int NumLegs() { return 4; } 

如果他们这样做，那么将调用新版本，如果他们没有，那么将使用基类版本，并将返回4。



CanFly存在同样的问题：接口方法不能被覆盖，因为它们没有;要有基类实现来覆盖。在这种情况下，只需删除关键字：

If they do, then the "new" version will be called, if they don't, then the base class version will be used, and 4 will be returned.

The same problem exists with CanFly: interface methods cannot be overridden as they don;t have a base class implementation to override. In this case, just remove the keyword:

public bool CanFly() { return true; } 

，你的错误就会消失。

and your errors will disappear.

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