如何将接口中的Java泛型类型参数限制为某些类 [英] How to restrict Java generics type parameter in interface to certain classes

问题描述

我正在创建一个类型化的接口定义，我想将type参数的可能值限制为一组类.这些类已经存在，不受我的控制.而且，它们之间没有通过类层次结构相互关联.

I am creating a typed interface defintion and I want to restrict the possible values for the type parameter to a set of classes. These classes are existing already and are not under my control. Also, they are not related to each other through the class hierarchy.

例如，我有三个类A，B，C.我的界面是 IMyFancyInterface< T> .如何限制此接口的实现者，并确保T仅是A，B或C?非常感谢.

So, for example, I have three classes A, B, C. My interface is IMyFancyInterface<T>. How can I restrict implementors of this interface and make sure that T is either A, B, or C only? Thanks a lot.

干杯

马丁

推荐答案

如果 A ， B 和 C 具有共同的超类型(假设它称为 Super )，那么您可以这样做:

If A, B and C have a common super-type (let's say it's called Super), then you could do:

public interface IMyFancyInterface<T extends Super> { .. }

这样，您应该始终使用类型参数来实现此接口，该类型参数是 Super 的子类型，即 A ， B 或 C .

This way you should always implement this interface with a type-parameter that is a sub-type of Super, i.e. A, B or C.

但是，如果 A ， B 和 C 没有通用的超级类型，则可以创建标记接口(一个没有抽象方法的接口)并使其实现.例如:

If, however, A, B and C don't have a common super-type, you could create a marker interface (an interface with no abstract methods) and make them implement it. For example:

public interface Marker { }

public class A implements Marker { }

public class B implements Marker { }

public class C implements Marker { }

这样，您就可以遵循我最初建议的方法:

This way you'd be able to follow the approach I initially suggested:

public interface IMyFancyInterface<T extends Marker> { .. }

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