Groovy def l = [1、2、3]作为BlockingQueue

问题描述

如果我将类似 def l = [1、2、3]的内容写为Socket 显然是胡说八道，我会得到:

If I write something like def l = [1, 2, 3] as Socket which is obviously nonsense, I get this:

org.codehaus.groovy.runtime.typehandling.GroovyCastException: Cannot cast object '[1, 2, 3]' with class 'java.util.ArrayList' to class 'java.net.Socket' 

那很有道理.

现在，我尝试一些不太冒险的事情:

Now I try something less adventurous:

import java.util.concurrent.BlockingQueue

def l = [1, 2, 3] as BlockingQueue
println l.class
println l

这不会引发异常，并显示以下内容:

This doesn't throw an exception, and prints the following:

class ArrayList1_groovyProxy
[1, 2, 3]

那么 ArrayList1_groovyProxy 是什么，为什么我可以将列表无误地投射到 BlockingQueue ，尽管它失败了( l 不会最终不会成为 BlockingQueue 实例)?

So what's ArrayList1_groovyProxy, and why am I able to cast the list to BlockingQueue without error despite the fact that it fails (l doesn't end up being an BlockingQueue instance)?

• 首先，我想指出 def l = [1、2、3]，因为List 运作良好，并生成了 ArrayList 尽管 List 和 BlockingQueue 都是接口.

• 第二，在Dónal的答案之后，我尝试了以下操作:

• First of all, I'd like to point out that def l = [1, 2, 3] as List works well, and produces a regualr instance of ArrayList despite the fact that both List and BlockingQueue are interfaces.

• Second, after Dónal's answer, I tried the following:

def l = [1, 2, 3] as BlockingQueue
assert l instanceof BlockingQueue
println l.class
println l

这打印了以下几行，没有抛出断言异常:

This printed the following lines and no assertion exceptions were thrown:

class ArrayList1_groovyProxy
[1, 2, 3]

但是，此行的确抛出 MissingMethodException :

l.offer(5)

所以断言以某种方式成功了，但是尝试将 l 用作BlockingQueue会引发异常.

So the assertion somehow succeeds, but trying to use l as a BlockingQueue throws an exception.

第三，如果我尝试 def l = [1、2、3]作为Map ，也会发生同样的情况这段代码:

Third, the same happens if I try def l = [1, 2, 3] as MapThis code:

def l = [1, 2, 3] as Map
assert l instanceof Map
println l
println l.getClass()

不产生任何错误并打印:

produces no errors and prints:

[1, 2, 3]
class ArrayList1_groovyProxy

推荐答案

这只是Groovy可爱.可以看到您正在尝试创建一个集合，但是无法弄清楚如何构造一个BlockingQueue.它回退到代理的ArrayList.如果您在左侧使用类型声明而不是"def"，那么它将被炸毁.再次，它变得很可爱，因为您使用的是def.烦人，不是吗?:)

It's just Groovy being cute. It's able to see that you're trying to create a collection, but it can't figure out how to construct a BlockingQueue. It's falling back to a proxied ArrayList. If you'd gone with a type declaration on the left side instead of a "def," it would have blown up. Again, it's getting cute because you're using a def. Annoying, isn't it? :)

这篇关于Groovy def l = [1、2、3]作为BlockingQueue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！