Java中无界的通配符 [英] Unbounded wildcards in Java

问题描述

无界通配符例如<？> 和一个有界通配符，其边界是 Object ，例如< ;?扩展对象> ？

Is there ever a difference between an unbounded wildcard e.g. <?> and a bounded wildcard whose bound is Object, e.g. <? extends Object>?

我记得有些地方在泛型的早期草稿中有所不同，但是找不到这个源代码。 / p>

I recall reading somewhere that there was a difference in the early drafts of generics, but cannot find that source anymore.

推荐答案

作为pedntry的一个要点，如果类/接口/构造函数/方法声明一个绑定（除<
$ b

As a point of pedntry, there is a difference if the class/interface/constructor/method declares a bound (other than extends Object).

interface Donkey<T extends Thing> { }

...
    Donkey<? extends Object> foo; // FAIL

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