模式，以弥补基于Java中的多态args缺乏运行时方法查找？ [英] Patterns to compensate for lack of runtime method lookup based on polymorphic args in Java?

问题描述

似乎Java无法根据参数的运行时类型选择最合适的方法实现，如文档此处。概括示例：

It seems that Java can't choose the most appropriate method implementation based on the runtime type of an argument, as documented here. Recapitulating the example:

class Superclass {}
class Subclass extends Superclass {}
class Test {
    public void aMethod(Superclass s) {...}
    public void aMethod(Subclass s) {...}
}

执行Test类的哪种方法取决于引用的类型，而不是实例的类型。同样，基于链接的示例：

Which method of the Test class is executed is determined based on the type of the reference, not the type of the instance. Again, based on the linked examples:

Test aTest = new Test();
Superclass aSuper = new Subclass();
test.aMethod(aSuper);

aMethod（Superclass s）那个执行，而不是 aMethod（子类s）。

我试图在侦听器模式上创建一个变体，其中侦听器通过接口插入，并且侦听器具有为接口的子类定义的方法。

I was trying to create a variation on the listener pattern, where listeners 'plug in' via an interface, and the listeners have methods defined for subclasses of the interfaces.

作为我的意思的一个简单示例，说我正在构建一个可以插入功能的闹钟。

As a quick example of what I mean, say I'm building an alarm clock that can have functionality plugged in.

我想到的上面的实现看起来像一个接口 Event ，子类 WakeUpEvent ，接口 EventListener 需要实现句柄（事件evt）。

The implementation for the above I had in mind would look like an interface Event, with a subclass WakeUpEvent, and an interface EventListener requiring implementation of handle(Event evt).

我希望创建一个实现no-op 句柄的类（Event evt）带有特定的句柄（WakeUpEvent evt）如果听众想要处理那种类型的事件。

I hoped to create a class implementing a no-op handle(Event evt) with a specific handle(WakeUpEvent evt) if the listener wanted to deal with that type of event.

当然，这种方法不会按原样运作 - 显而易见的解决方案ion是运行时 instanceof 检查 - yuk。

Of course, this approach won't work as-is - the obvious solution is runtime instanceof checks - yuk.

我是否可以使用任何模式或方法来获取行为我想要？

Are there any patterns or approaches that I can use to get the behaviour I want?

推荐答案

这些情况是我想到访客或双重调度模式。

These situations are when I think of Visitor or double dispatch pattern.

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