仅在运行时知道通用类型时如何指定通用类型？ [英] How to specify generic type when the type is only known at runtime?

问题描述

我需要一些代码来动态生成一组子类的泛型类型为1的泛型对象： keyEvent ， mouseEvent 或 appEvent ，这些都扩展了事件。因此，我的通用类 EventFunction 需要一个模板，但是在接收到该事件之前，我不知道类的类型，因此可以执行以下操作：

I have some code that I need to generate a generic object on the fly with the generic type of 1 of a set of subclasses: e.g. keyEvent, mouseEvent or appEvent, these all extend event. So, my generic class EventFunction requires a template, however I dont know what the class type is until I recieve the event, so is there a way to do the following:

Event event = new KeyEvent(); // FOR EXAMPLE RECIEVING A KEY EVENT
// Require an EventFunction with that event class as the generic type
EventFunction<event.getClass()> func = new EventFunction<event.getClass()>(event);

如何执行上述操作：即即时指定通用值？

How do I do the above: i.e. specify generic values on the fly?

推荐答案

以下代码段可能会对您有所帮助：

The following snippet may help you:

class Event { }

class FooEvent extends Event { }

class EventFunction<T extends Event> {
    public EventFunction(T event) { }
}

class EventFunctionFactory {
   public <T extends Event> EventFunction<T> buildFunction(T event) {
       if (event.getClass().equals(FooEvent.class)) {
            System.out.println("A new FooEventFunction!");          
            return new EventFunction<T>(event);
       }
       else {
           return null;
       }
   }
}

用法如下：

    EventFunctionFactory factory = new EventFunctionFactory();
    Event foo = new FooEvent();
    EventFunction<Event> function = factory.buildFunction(foo);

这里有一个摘要

< a href = http://tpcg.io/bMNbkd rel = nofollow noreferrer> http://tpcg.io/bMNbkd

这篇关于仅在运行时知道通用类型时如何指定通用类型？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！