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。

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。

作为一个。net开发人员，你完全有可能一辈子都不编写自己的接口。毕竟，没有它们，我们也活了几十年，我们的语言仍然是图灵完备的。

我不能告诉你为什么你需要接口，但我可以给你一个我们在当前项目中使用它们的列表:

在我们的插件模型中，我们通过接口加载插件，并将该接口提供给插件编写者以使其遵循。 在我们的机间消息传递系统中，消息类都实现了一个特定的接口，并使用该接口“解包装”。 我们的配置管理系统定义了一个用于设置和检索配置设置的接口。 我们使用一个接口来避免讨厌的循环引用问题。(如果没有必要，就不要这样做。)

我想如果有一个规则，那就是当你想在一个is-a关系中对几个类进行分组，但你不想在基类中提供任何实现时使用接口。

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。

别太担心。很多开发人员很少需要编写接口。您将经常使用. net框架中可用的接口，但如果您觉得没有必要在短时间内编写一个接口，这也没什么好奇怪的。

我经常给别人的例子是，如果你有一个帆船职业和一个毒蛇职业。它们分别继承了Boat类和Car类。现在假设您需要遍历所有这些对象并调用它们的Drive()方法。你也可以编写如下代码:

if(myObject is Boat)
    ((Boat)myObject).Drive()
else
    if (myObject is Car)
        ((Car)myObject).Drive()

这样写会简单得多:

((IDrivable)myObject).Drive()

它还允许您执行模拟单元测试(. net)。如果您的类使用接口，您可以在单元测试中模拟对象，并轻松地测试逻辑(无需实际触及数据库或web服务等)。

http://www.nmock.org/