我可以静态导入私有子类吗？

Question

I have an enum which is private, not to be exposed outside of the class. Is there anyway I can do a static import of that type, so that I don't have to type the enum type each time? Or is there a better way to write this? Example:

package kip.test;

import static kip.test.Test.MyEnum.*; //compile error

public class Test
{
  private static enum MyEnum { DOG, CAT }

  public static void main (String [] args)
  {
    MyEnum dog = MyEnum.DOG; //this works but I don't want to type "MyEnum"
    MyEnum cat = CAT; //compile error, but this is what I want to do
  }
}

Answer 1

You can use the no-modifier access level, ie

enum MyEnum { DOG, CAT }

MyEnum will not be visible to classes from other packages neither from any subclass. It is the closest form of private, yet letting you avoid explicitly referencing MyEnum .

Answer 2

Or is there a better way to write this?

If your main goals are to reference the items without their qualifying enum identifier, and maintain this list privately, you could scrap the enum type altogether and use ordinary private static constants.

Answer 3

Considering that you can access the field fully qualified, I would say that it is a bug in the compiler (or language spec) that you cannot statically import it.

I suggest that you make the enumeration package-protected.

Answer 4

It may (or may not) be reasonable to move some of the code into (static) methods of the enum.

If pressed, you could duplicate the static fields in the outer class.

private static final MyEnum CAT = MyEnum.CAT;
private static final MyEnum DOG = MyEnum.DOG;

Icky, but a possibility.

Answer 5

不，这几乎就是private所有。

Answer 6

You could simply write your code inside the enum itself.

public enum MyEnum {
DOG, CAT;
public static void main(String[] args) {
    MyEnum dog = MyEnum.DOG; // this works but I don't want to have to type
                                // MyEnum
    MyEnum cat = CAT; // compile error, but this is what I want to do
}
 }

The other place where private enums can be references without their class is in a switch statement:

private static enum MyEnum {
    DOG, CAT
}

public static void main(String[] args) {
    MyEnum e = null;
    switch (e) {
    case DOG:
    case CAT:
    }
}