在Java接口中声明参数子类型，在Java实现方法中使用子类型

发布于 2024-10-14 15:02:23 字数 399 浏览 2 评论 0原文

我想在接口中声明一个方法，其中实现类中定义的方法的参数可以是特定 java 类的子类型，例如：

interface Processor{
      processRequest( Request r);
}

public class SpecialRequest extends Request{...}

public class SpecialProcessor implements Processor{

      processRequest(SpecialRequest r){...}
}

但我在 SpecialProcessor 中收到错误，因为它没有正确实现 Processor 接口。我可以在 Processor 接口中更改哪些内容以允许 SpecialProcessor 中的定义起作用？

原文

I want to declare a method in an interface where the parameter of the method defined in implementing classes can be a subtype of a specific java class for example:

interface Processor{
      processRequest( Request r);
}

public class SpecialRequest extends Request{...}

public class SpecialProcessor implements Processor{

      processRequest(SpecialRequest r){...}
}

but I get errors in the SpecialProcessor because it doesn't properly implement the Processor interface. What can I change in the Processor interface to allow the definition in the SpecialProcessor to work?

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陌生 2024-10-21 15:02:23

您可以输入处理器：

public interface Processor<R extends Request> {
    void processRequest(R r);
}


public class SpecialProcessor implements Processor<SpecialRequest> {
    public void processRequest(SpecialRequest r) {
       ...
    }
}

You can type Processor:

public interface Processor<R extends Request> {
    void processRequest(R r);
}


public class SpecialProcessor implements Processor<SpecialRequest> {
    public void processRequest(SpecialRequest r) {
       ...
    }
}

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合久必婚 2024-10-21 15:02:23

没错 - 请记住，调用者不应该知道正在使用接口的具体实现。他们只知道他们可以将Request（任何请求）传递给processRequest，而您的实现对参数施加了更严格的约束，导致某些方法调用的类型不正确。

如果你想这样做，你需要向接口添加一个通用参数，如下所示：

interface Processor<R extends Request> {
    void processRequest(R r);
}

public class SpecialProcessor implements Processor<SpecialRequest> {

    public void processRequest(SpecialRequest r) { ... }

}

这样，想要传递“正常”请求的调用者将必须声明一个 Processor - 并且您的 SpecialProcessor 不再与此绑定匹配，因此无法分配，并且将在编译时正确拒绝。自己处理特殊请求的调用者可以使用 Processor变量/字段，您的类可以分配给该变量/字段。

That's right - remember that a caller shouldn't know what specific implementation of the interface is being used. They just know that they can pass a Request (any Request) to processRequest, whereas your implementation is imposing a stricter constraint on the argument that would cause certain method calls not to be type-correct.

If you want to do this, you'll need to add a generic parameter to the interface, something like the following:

interface Processor<R extends Request> {
    void processRequest(R r);
}

public class SpecialProcessor implements Processor<SpecialRequest> {

    public void processRequest(SpecialRequest r) { ... }

}

This way, callers that want to pass in "normal" requests will have to declare a variable/field of type Processor<Request> - and your SpecialProcessor no longer matches this bound, so cannot be assigned, and will correctly be rejected at compile-time. Callers that are dealing with special requests themselves can use a Processor<SpecialRequest> variable/field, which your class can be assigned to.

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