Cannot `import static` static inner class?

问题

I have a class A with a static inner class inside it called B:

import static A.B.*;

class A {
    static class B {
        static int x;
        static int y;
    }
    public static void main(String[] args) {
        System.out.println(x);
    }
}

I want to static import everything in B, but it wont work:

$ javac A.java
A.java:1: package A does not exist
import static A.B.*;
               ^
A.java:9: cannot find symbol
symbol  : variable x
location: class A
        System.out.println(x);
                           ^
2 errors

Why?

回答1:

This won't work if A is in the default package. However, you could add a package declaration:

package mypackage;

and use

import static mypackage.A.B.*;

The static import syntax from from the JLS is given:

SingleStaticImportDeclaration: import static TypeName . Identifier ;

where TypeName is required to be full qualified.

In Using Package Members the static import syntax is given with package name included:

import static mypackage.MyConstants.*;

It is recommended to use static imports very sparingly.

回答2:

It should be

import <the-package-for-the-class-A>.A.B.*;

If A is in the default package, this will fail.

Last, it's not a good practice to import *. Just import only the things that you need, in this case - import static <the-package-for-the-class-A>.A.B.x; if you're gonna use only the x variable.

来源：https://stackoverflow.com/questions/16595847/cannot-import-static-static-inner-class