Java将接口转换为类 [英] Java cast interface to class

问题描述

我有一个关于接口和类实现接口的问题。

I have a question about interface and class implementing interface.

这是我的代码：

interface iMyInterface {
    public iMethod1();
}

public class cMyClass implements iMyInterface {
    public iMethod1() {
        // some code
    }
    protected iMethod2() {
        // some code
    }
}

以创建 iMyInterface 的实例：

iMyInterface i = new cMyClass();
i.iMethod1();

没关系，但如何调用 iMethod2 $ c>从我的接口实例？这是工作和安全：

It's ok, but how can I call iMethod2() from my interface instance? Is this working and safe:

((cMyClass)i).iMethod2();

感谢您的帮助。

推荐答案

是的，这将工作（如果您更改 cMyClass 的声明以实现 iMyInterface ）并且它是安全的，只要引用真的 是指 cMyClass 的实例。

Yes, that will work (if you change the declaration of cMyClass to implement iMyInterface) and it's safe so long as the reference really does refer to an instance of cMyClass.

但是，这是一个糟糕的主意。使用接口的全部要点是能够使用任何实现 - 它将抽象与实现分开。如果你需要一个特定的实现，你也可以使 i 的类型只是 cMyClass

However, it's a generally bad idea. The whole point of using an interface is to be able to work with any implementation - it's to separate the abstraction from the implementation. If you're then going to require a specific implementation, you might as well make the type of i just cMyClass to start with.

因此，假设不是自己调用 cMyClass 构造函数， c $ c> iMyInterface - 这是一个坏主意，转换到 cMyClass 在那一点，因为它可以是一个不同实现接口。

So suppose instead of calling the cMyClass constructor yourself, you receive a method parameter of type iMyInterface - it's a bad idea to cast to cMyClass at that point, as it could be a different implementation of the interface.

（另一个注意事项是，开始遵循Java命名约定是一个好主意，它规定类和接口应该是Pascal-cased - 因此请分开 c 和 i 前缀。）

(On a separate note, it's a good idea to start following Java naming conventions, which state that classes and interfaces should be Pascal-cased - so ditch the c and i prefixes.)

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