如何在Java中找出标识符的声明类型？ [英] How to find out the declared type of an identifier in Java?

问题描述

我有一个简单的类从另一个简单的类Fruit扩展。

I have a simple class Apple extends from another simple class Fruit.

在运行时，我可以使用

Fruit fruit = new Apple();

fruit.getClass();

获取水果对象的实际类型，即Apple.class。

to get the actual type of fruit object, which is Apple.class.

我还可以使用水果实例的Apple 和水果实例来验证这个水果对象是苹果或水果的一个实例。这两个表达式都返回true，这是正常的。

I could also use fruit instanceof Apple, and fruit instanceof Fruit to verify if this fruit object is an instance of Apple or Fruit. Both of these 2 expressions return true, which is normal.

但是有一种方法可以精确地确定 fruit identifier？在这种情况下是水果。

But is there a way to determine precisely the declared type of fruit identifier? Which in this case is Fruit.

推荐答案

一个关于 fruit 的变量声明的问题，而不是对象的实际运行时类型（这是 Apple 案件）。

You're actually asking a question about the variable declaration of fruit rather than the actual runtime type of the object (which is an Apple in this case).

我认为这是一个坏主意：你只是声明了变量，告诉编译器它是一个水果

I think this is in general a bad idea: you just declared the variable and told the compiler that it is a Fruit, so why do you need to now need to find this out?

为了更多地混淆事情，值得注意的是，你也可以有多个变量与不同的声明的类型引用同一个对象（它仍然是一个苹果）：

Just to confuse matters even more, it's worth noting that you can also have multiple variables with different declared types referencing the same object (which is still an Apple):

Fruit fruit = new Apple(); // fruit declared as Fruit, but refers to an Apple
Object thing = fruit;      // thing declared as Object, refers to the same Apple

如果你真的想知道类型，那么你有几个选项：

If you really want to find out the declared type, then you have a few options:

• 使 fruit


• 对源代码进行一些处理以找到变量声明


• 对编译的字节码进行一些处理找到声明类型（虽然积极的编译器可能甚至优化编译时声明，例如在意识到水果只能在这个代码中是一个苹果）。

我认为所有这些都是很丑陋的，所以我的一般建议是不要做。

I think all of these are pretty ugly, so my general advice would be "don't do it".

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