为什么不能在一个方法中本地声明枚举？ [英] Why can't enums be declared locally in a method?

问题描述

今天，我发现自己编写这样的东西...

  public class LocalEnums {
 
 public LocalEnums（）{
} 
 
 public void foo（）{
枚举LocalEnum {
 A，B，C 
}; 
 
 // .... 
 // class LocalClass {} 
 
} 
} 
  / pre> 
 
 
当编译器报告本地枚举错误时，我感到非常惊讶：
 
 
会员枚举LocalEnum不能
本地
 
 
为什么不能将枚举本地声明为类？
 
 
 
我发现这在某些方面非常有用的情况。在我工作的情况下，其余的代码不需要知道关于枚举的任何内容。。
 
 
 
是否有任何结构/设计冲突，这解释了为什么这是不可能的，或者这可能是Java的未来功能？
解决方案
 枚举是静态嵌套类，因为它们定义静态成员变量（枚举值），这是不允许内部类： http://docs.oracle.com/javase/specs/jls/se7/html/jls-8.html#jls-8.1.3  
 
 
 
 更新：我正在查看 JLS （ java语言规范），了解更多有关限制的详细信息静态嵌套类，并没有找到它（虽然它可能在那里，隐藏在不同的主题下）。从纯实施的角度来看，没有理由不能做到这一点。所以我怀疑这是一个语言哲学问题：不应该做，所以不会得到支持。但是我不在，所以这是纯粹的猜测。
 
 
 
 作为评论：如果你的方法足够大，他们需要自己的枚举那么这是一个强有力的标志，你需要重构。
 
Today, I found myself coding something like this ...
public class LocalEnums {

    public LocalEnums() {
    }

    public void foo() {
        enum LocalEnum {
            A,B,C
        };

        // ....
        // class LocalClass { }

    }
}
and I was kind of surprised when the compiler reported an error on the local enum:

  
The member enum LocalEnum cannot be
  local
Why can't enums be declared local like classes?

I found this very useful in certain situations. In the case I was working, the rest of the code didn't need to know anything about the enum.

Is there any structural/design conflict that explains why this is not possible or could this be a future feature of Java?
解决方案
Enums are static nested classes because they define static member variables (the enum values), and this is disallowed for inner classes: http://docs.oracle.com/javase/specs/jls/se7/html/jls-8.html#jls-8.1.3

Update: I was looking through the JLS (java language specification) for more detail on the restrictions of static nested classes, and didn't find it (although it's probably there, hidden under a different topic). From a pure implementation perspective, there's no reason that this couldn't be done. So I suspect that it was a language philosophy issue: it shouldn't be done, therefore won't be supported. But I wasn't there, so that's pure speculation.

As a comment: if your methods are large enough that they require their own enums, then it's a strong sign that you need refactoring.

                        
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