为什么 Java 不允许 Throwable 的泛型子类? [英] Why doesn't Java allow generic subclasses of Throwable?

问题描述

根据 Java 语言规范，第 3 版:

这是一个编译时错误，如果一个泛型class 是 Throwable 的直接或间接子类.

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

我想了解为什么做出这个决定.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，泛型只是编译时的语法糖，它们无论如何都会在 .class 文件中被转换为 Object，因此有效地声明泛型类就好像其中的所有内容都是 Object.如果我错了，请纠正我.)

(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

如mark所说，类型不可具体化，在以下情况下会出现问题:

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 和 SomeException 都被擦除为同一类型，JVM 无法区分异常实例，因此没有判断应该执行哪个 catch 块的方法.

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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