As several people have probably already answered, interfaces can be used to enforce certain behaviors between classes that will not implement those behaviors the same way. So by implementing an interface you are saying that your class has the behavior of the interface. The IAnimal interface would not be a typical interface because Dog, Cat, Bird, etc. classes are types of animals, and should probably extend it, which is a case of inheritance. Instead, an interface would be more like animal behavior in this case, such as IRunnable, IFlyable, ITrainable, etc.

接口有很多好处，其中一个关键就是可插拔性。例如，声明一个具有List参数的方法将允许传入实现List接口的任何东西，允许开发人员在以后删除和插入不同的列表，而不必重写大量代码。

您可能永远不会使用接口，但如果您正在从头开始设计一个项目，特别是某种类型的框架，您可能会想要熟悉它们。

我建议大家阅读Coad、Mayfield和Kern撰写的《Java设计》中关于接口的章节。它们比一般的介绍性文本解释得好一点。如果你不使用Java，你可以只阅读本章的开头，主要是一些概念。

一旦你需要为你的类强制一个行为，你应该定义一个接口。

动物的行为可能包括走、吃、跑等。因此，您将它们定义为接口。

另一个实际的例子是ActionListener(或Runnable)接口。您可以在需要跟踪特定事件时实现它们。因此，您需要在类(或子类)中提供actionPerformed(Event e)方法的实现。类似地，对于Runnable接口，提供公共void run()方法的实现。

此外，您可以让任意数量的类实现这些接口。

使用接口(在Java中)的另一个实例是实现c++中提供的多重继承。

一些非编程示例可能帮助您了解接口在编程中的适当使用。

There's an interface between electrical devices and the electricity network - it's the set of conventions about the shape of the plugs and sockets and the voltages/currents across them. If you want to implement a new electrical device, as long as your plug follows the rules it will be able to get services from the network. This makes extensibility very easy and removes or lowers the costs of coordination: you don't have to notify the electricity provider about how your new device works and come to a separate agreement about how to plug your new device into the network.

各国都有标准的铁路轨距。这使得铺设铁轨的工程公司和建造在这些铁轨上运行的列车的工程公司之间实现了分工，并使铁路公司有可能在不重新设计整个系统的情况下更换和升级列车。

The service a business presents to a client can be described as an interface: a well defined interface emphasises the service and hides the means. When you put a letter in a mailbox, you expect the postal system to deliver the letter within a given time but you have no expectations about how the letter is delivered: you don't need to know, and the postal service has the flexibility to choose the means of delivery that best meets the requirements and current circumstances. An exception to this is the ability of customers to choose airmail - that's not the kind of interface a modern computer programmer would have designed, since it reveals too much of the implementation.

来自自然的例子:我不太喜欢eats()， makesSound()， moves()等例子。它们确实描述了行为，这是正确的，但它们没有描述交互以及它们是如何被启用的。在自然界中，使相互作用成为可能的界面的一个明显的例子是与繁殖有关的，例如一朵花为蜜蜂提供了一个特定的界面，以便授粉能够发生。

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.

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。

一个代码示例(结合了Andrew的代码和我的额外的关于“接口的目的是什么”的代码)，也说明了为什么在不支持多重继承的语言(c#和java)上接口而不是抽象类:

interface ILogger
{
    void Log();
}
class FileLogger : ILogger
{
    public void Log() { }
}
class DataBaseLogger : ILogger
{
    public void Log() { }
}
public class MySpecialLogger : SpecialLoggerBase, ILogger
{
    public void Log() { }
}

注意，FileLogger和DataBaseLogger不需要接口(可以是Logger的抽象基类)。但是考虑到您需要使用第三方记录器，它迫使您使用基类(假设它公开了您需要使用的受保护的方法)。由于语言不支持多重继承，您将无法使用抽象基类方法。

底线是:尽可能使用接口来获得代码的额外灵活性。您的实现不那么受约束，因此它能更好地适应变化。