接口中的构造函数？ [英] Constructor in an Interface?

问题描述

我知道在界面中定义构造函数是不可能的。但我想知道为什么，因为我认为它可能非常有用。

I know it's not possible to define a constructor in an interface. But I'm wondering why, because I think it could be very useful.

所以你可以确定类中的某些字段是为这个接口的每个实现定义的。

So you could be sure that some fields in a class are defined for every implementation of this interface.

例如，考虑以下消息类：

For example consider the following message class:

public class MyMessage {

   public MyMessage(String receiver) {
      this.receiver = receiver;
   }

   private String receiver;

   public void send() {
      //some implementation for sending the mssage to the receiver
   }
}

如果为这个类定义一个接口，以便我可以有更多的类来实现消息接口，我只能定义send方法而不是构造函数。那么我怎样才能确保这个类的每个实现都有一个接收器集？如果我使用像 setReceiver（String receiver）这样的方法，我无法确定是否真的调用了这个方法。在构造函数中，我可以确保它。

If a define an interface for this class so that I can have more classes which implement the message interface, I can only define the send method and not the constructor. So how can I ensure that every implementation of this class really has an receiver set? If I use a method like setReceiver(String receiver) I can't be sure that this method is really called. In the constructor I could ensure it.

推荐答案

采取你所描述的一些事情：

Taking some of the things you have described:

所以你可以确定一个类中的某些字段是为每个实现这个接口的
定义的。

"So you could be sure that some fields in a class are defined for every implementation of this interface."

如果为这个类定义一个接口，这样我可以有更多的
类来实现消息接口，我只能定义
send方法而不是构造函数

"If a define a Interface for this class so that I can have more classes which implement the message interface, I can only define the send method and not the constructor"

......这些要求正是抽象类适用于。

...these requirements are exactly what abstract classes are for.

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