接口实例VS类的实例 [英] Interface instantiation vs class instantiation

问题描述

可能有人请helpme明白，如果下面的代码相同。如果不是出了什么阶级和interfance实例之间的区别。

Could someone please helpme to understand if the following codes are same. If not what's the difference between class and interfance instantiation.

IUnityContainer container = new UnityContainer()
UnityContainer container = new UnityContainer()

据我了解Inteface只有方法签名，如果接口已被执行3班。不太清楚其中3实例将由上述第一条语句创建。

As far as I understand Inteface has only method signature and if the interface has been implemented by 3 classes. Not too sure which of the 3 instance would be created by first statement above.

三江源。

推荐答案

接口不能被定义实例化。你总是实例化的具体类。

Interfaces can't be instantiated by definition. You always instantiate a concrete class.

所以的两个的语句您的实例实际类型为 UnityContainer 。

So in both statements your instance is actually of type UnityContainer.

的区别是第一个声明，至于C＃而言，你的容器是一些农具 IUnityContainer ，这可能具有 UnityContainer 不同的API。

The difference is for the first statement, as far as C# is concerned, your container is something that implements IUnityContainer, which might have an API different from UnityContainer.

考虑：

interface IAnimal 
{
    void die();
}

class Cat : IAnimal 
{
    void die() { ... }
    void meow() { ... }
}

现在：

IAnimal anAnimal = new Cat();
Cat aCat= new Cat();

C＃糊涂账 anAnimal.die（）的作品，因为死（）在 IAnimal 。但它不会让你做 anAnimal.meow（），即使它是一个猫，而 ACAT 可以调用这两种方法。

C# knows for sure anAnimal.die() works, because die() is defined in IAnimal. But it won't let you do anAnimal.meow() even though it's a Cat, whereas aCat can invoke both methods.

当您使用的接口为你的类型你是，在某种程度上，丢失信息。

When you use the interface as your type you are, in a way, losing information.

不过，如果你有其他类狗也实现 IAnimal ，您 anAnimal 可以引用狗实例为好。这是一个接口的供电;你可以给他们实现它的任何类。

However, if you had another class Dog that also implements IAnimal, your anAnimal could reference a Dog instance as well. That's the power of an interface; you can give them any class that implements it.

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