当您希望能够对多个类型使用单个变量，但所有这些类型通过接口声明实现相同的方法时，Jimmy是正确的。然后你可以在接口类型变量上调用它们的main方法。

然而，使用接口还有第二个原因。当项目架构师和实现编码员是不同的人时，或者有几个实现编码员和一个项目经理。负责人可以编写一大堆接口，并查看系统的互操作，然后让开发人员用实现类填充接口。这是确保多人编写兼容类的最佳方法，而且他们可以并行地完成。

把接口想象成一个契约。这是一种说法，“这些类应该遵循这些规则。”

所以在IAnimal的例子中，它是一种说，“我必须能够在实现IAnimal的类上调用Run, Walk等。”

为什么这个有用?您可能希望构建一个函数，该函数依赖于必须能够在对象上调用Run和Walk这一事实。你可以有以下内容:

public void RunThenWalk(Monkey m) {
    m.Run();
    m.Walk();
}

public void RunThenWalk(Dog d) {
    d.Run();
    d.Walk();
}

．.． 对所有你知道能跑能走的物体重复这一步骤。然而，在你的IAnimal接口中，你可以像下面这样定义函数:

public void RunThenWalk(IAnimal a) {
    a.Run();
    a.Walk();
}

通过根据接口编程，您实际上是信任类来实现接口的目的。所以在我们的例子中，想法是“我不在乎他们怎么跑和走，只要他们能跑和走。”只要他们履行协议，我的RunThenWalk就有效。它在不了解任何其他课程的情况下运行得很好。”

在这个相关的问题上也有很好的讨论。

I like Jimmy's answer a lot, but I feel I need to add something to it. The key to the whole thing is the "able" in IProcessable . It indicates a capability (or property, but meaning "intrinsic quality", not in the sense of C# properties) of the object that implements the interface. IAnimal is probably not a good example for an interface, but IWalkable might be a good interface to have if your system has many things that can walk. You might have classes derived from Animal such as Dog, Cow, Fish, Snake. The first two would probably implement IWalkable, the latter two don't walk, so they wouldn't. Now you ask "why not just have another superclass, WalkingAnimal, that Dog and Cow derive from?". The answer is when you have something completely outside the inheritance tree that also can walk, such as a robot. Robot would implement IWalkable, but probably wouldn't derive from Animal. If you want a list of things that can walk, you type it as IWalkable and you can put all walking animals plus robots in the list.

现在，将IWalkable替换为IPersistable这样更像软件的东西，这样的类比就更接近你在实际程序中看到的情况了。

我喜欢军队的比喻。

中士不在乎你是软件开发人员、音乐家还是律师。 你被当作士兵对待。

对于中士来说，不去操心与他一起工作的人的具体细节更容易， 把每个人都当作抽象的士兵(…如果他们表现得不像孩子，就要惩罚他们)。

人们像士兵一样行动的能力被称为多态性。

接口是帮助实现多态的软件结构。

为了实现简单，需要抽象细节，这就是你问题的答案。

Polymorphism, which etymologically means "many forms," is the ability to treat an object of any subclass of a base class as if it were an object of the base class. A base class has, therefore, many forms: the base class itself, and any of its subclasses. (..) This makes your code easier for you to write and easier for others to understand. It also makes your code extensible, because other subclasses could be added later to the family of types, and objects of those new subclasses would also work with the existing code.

如果浏览. net Framework程序集并深入到任何标准对象的基类中，您将注意到许多接口(名为ISomeName的成员)。

Interfaces are basically for implementing frameworks, large or small. I felt the same way about interfaces until I wanted to write a framework of my own. I also found that understanding interfaces helped me learn frameworks much more rapidly. The moment that you want to write a more elegant solution for just about anything, you will find that an interface makes a lot of sense. It's like a method of letting a class put on the appropriate clothes for the job. More importantly, interfaces allow systems to become much more self-documenting, because complex objects become less complex when the class implements interfaces, which helps to categorize its functionality.

类在希望能够显式或隐式地参与框架时实现接口。例如，IDisposable是一个公共接口，它为流行且有用的Dispose()方法提供方法签名。在框架中，您或其他开发人员需要知道的关于类的所有信息是，如果它实现了IDisposable，那么您就知道((IDisposable)myObject). dispose()可用于清理目的。

经典示例:在没有实现IDisposable接口的情况下，你不能在c#中使用"using()"关键字构造，因为它要求任何指定为参数的对象都可以隐式转换为IDisposable。

复杂的例子: 一个更复杂的例子是System.ComponentModel.Component类。这个类同时实现了IDisposable和IComponent。大多数(如果不是全部的话)具有与之关联的可视化设计器的. net对象实现了IComponent，以便IDE能够与组件交互。

CONCLUSION: As you become more familiar with the .NET Framework, the first thing you will do when encountering a new class in the Object Browser or within the .NET Reflector (free) tool (http://www.red-gate.com/products/reflector/) is to check to see which class it inherits from and also the interfaces that it implements. .NET Reflector is even better than the Object Browser because it lets you see the Derived classes as well. That allows you to learn about all objects that derive from a particular class, thereby potentially learning about framework functionality that you did not know existed. This is particularly significant when updated or new namespaces are added to the .NET Framework.

我偶尔也会使用接口，下面是我最新的用法(名称已经概括了):

我在WinForm上有一堆需要将数据保存到业务对象的自定义控件。一种方法是分别调用每个控件:

myBusinessObject.Save(controlA.Data);
myBusinessObject.Save(controlB.Data);
myBusinessObject.Save(controlC.Data);

这个实现的问题是，每当我添加一个控件，我必须进入我的“保存数据”方法，并添加新的控件。

我改变了我的控件来实现一个ISaveable接口，它有一个方法SaveToBusinessObject(…)，所以现在我的“保存数据”方法只是通过控件迭代，如果它发现一个是ISaveable，它调用SaveToBusinessObject。所以现在当需要一个新的控件时，所有人要做的就是在该对象中实现ISaveable(并且永远不要触及其他类)。

foreach(Control c in Controls)
{
  ISaveable s = c as ISaveable;

  if( s != null )
      s.SaveToBusinessObject(myBusinessObject);
}

接口通常未被意识到的好处是本地化修改。定义之后，您很少会更改应用程序的整体流程，但通常会在细节级别上进行更改。当您将细节保存在特定对象中时，ProcessA中的更改将不会影响ProcessB中的更改。(基类也有这个好处。)

编辑:另一个好处是行动的专一性。就像在我的例子中，我所要做的就是保存数据;我不关心它是什么类型的控件，或者它是否可以做任何其他事情——我只想知道我是否可以保存控件中的数据。它使我的保存代码非常清晰——没有检查它是否为文本、数字、布尔值或任何东西，因为自定义控件处理所有这些。