为什么Java不允许Throwable的通用子类？ [英] Why doesn't Java allow generic subclasses of Throwable?

问题描述

根据 Java语言识别，第3版：

如果通用类是 Throwable 的直接或间接子类，则是编译时错误。

It is a compile-time error if a generic class is a direct or indirect subclass of Throwable.

我想了解为什么这个决定已经完成。通用异常有什么问题？

I wish to understand why this decision has been made. What's wrong with generic exceptions?

（据我所知，泛型是简单的编译时语法糖，它们将被翻译成 Object 无论如何，在 .class 文件中，所以有效地声明一个通用类就好像它的一切都是一个 Object 如果我错了，请更正我。）

(As far as I know, generics are simply compile-time syntactic sugar, and they will be translated to Object anyway in the .class files, so effectively declaring a generic class is as if everything in it was an Object. Please correct me if I'm wrong.)

推荐答案

正如Mark所说，这些类型不可以，这是以下情况的问题：

As mark said, the types are not reifiable, which is a problem in the following case:

try {
   doSomeStuff();
} catch (SomeException<Integer> e) {
   // ignore that
} catch (SomeException<String> e) {
   crashAndBurn()
}

SomeException< Integer> 和 SomeException< String> 被删除为相同类型，JVM无法区分异常实例，因此无法确定哪个 catch 块应该执行。

Both SomeException<Integer> and SomeException<String> are erased to the same type, there is no way for the JVM to distinguish the exception instances, and therefore no way to tell which catch block should be executed.

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