内部 class 允许静态字段和非常量静态表达式 - 为什么？

Question

根据 JLS :

An inner class is a nested class that is not explicitly or implicitly declared static. Inner classes may not declare static initializers or member interfaces.

但是我下面的代码编译成功了。

class A {
    interface B { 
        class C { // Inner class having static variables.
            static int d; // Static variable
            static {
            }
        }
    }
}

谁能帮我理解这种行为

Answer 1

嵌套接口是隐式静态的，并且本身没有非静态上下文，这就是 C 是隐式静态的原因。

Answer 2

你可以在一个接口里面定义一个class。在接口内部，内部 class 隐式 public 是静态的。 ... Interfaces may contain member type declarations 接口中的成员类型声明是隐式静态的并且 public.

所以我们不能将非静态成员声明到静态块、静态方法 或 static class.

Answer 3

找到相同的 JLS 规范：

8.5.2 - "Member interfaces are always implicitly static"

9.5 - "Interfaces may contain member type declarations (§8.5). A member type declaration in an interface is implicitly static and public"

这意味着上面的代码在道德上等同于（隐式修饰符以大写字母书写）：

class A {
    STATIC interface B {
        PUBLIC STATIC class C { //It's a static class - that's why static members are legal (like a toplevel class but nested)
            static int d; //Static variable
            static {} //Static initializer

        }
    }
}

内部 class 允许静态字段和非常量静态表达式 - 为什么？

Inner class allows static fields and non constant static expression - Why?

java

inner-classes