对 Java 枚举使用类型别名

发布于 2024-08-09 00:42:37 字数 701 浏览 0 评论 0原文

我想实现类似于scala如何将Map定义为两者预定义的类型和对象的东西。在 Predef 中：

type Map[A, +B] = collection.immutable.Map[A, B]
val Map = collection.immutable.Map //object Map

但是，我想使用 Java enum （来自共享库）来执行此操作。例如，我有一些全局别名：

type Country = my.bespoke.enum.Country
val Country = my.bespok.enum.Country //compile error: "object Country is not a value"

这样做的原因是我希望能够使用如下代码：

if (city.getCountry == Country.UNITED_KINGDOM) //or...
if (city.getCountry == UNITED_KINGDOM)

但是，在同时导入我的类型别名时这是不可能的。 注意：如果我没有声明预定义类型并导入它，此代码将正常工作！我可以在此处使用一些语法来实现此目的吗？

原文

I would like to achieve something similar to how scala defines Map as both a predefined type and object. In Predef:

type Map[A, +B] = collection.immutable.Map[A, B]
val Map = collection.immutable.Map //object Map

However, I'd like to do this using Java enums (from a shared library). So for example, I'd have some global alias:

type Country = my.bespoke.enum.Country
val Country = my.bespok.enum.Country //compile error: "object Country is not a value"

The reason for this is that I'd like to be able to use code like:

if (city.getCountry == Country.UNITED_KINGDOM) //or...
if (city.getCountry == UNITED_KINGDOM)

Howver, this not possible whilst importing my type alias at the same time. Note: this code would work just fine if I had not declared a predefined type and imported it! Is there some syntax I can use here to achieve this?

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我一向站在原地 2024-08-16 00:42:37

在 Scala 中只需使用 import：

import mypackage.Country
import mypackage.Country._

val c = Country.FRANCE
// With pattern matching:
c match {
  case UK => println("UK")
  case FRANCE => println("FRANCE")
}
// Or with an if:
if (c == FRANCE) println("FRANCE")

对于 Java 使用静态导入：

package mypackage;

import static mypackage.Country.*;

public class Test {
    public static void main(String[] args) {
        Country c = UK;
        if (c == FRANCE) {
            System.out.println("Ok");
        }
    }
}

enum Country {FRANCE, UK};

In Scala just use import:

import mypackage.Country
import mypackage.Country._

val c = Country.FRANCE
// With pattern matching:
c match {
  case UK => println("UK")
  case FRANCE => println("FRANCE")
}
// Or with an if:
if (c == FRANCE) println("FRANCE")

And for Java use static import:

package mypackage;

import static mypackage.Country.*;

public class Test {
    public static void main(String[] args) {
        Country c = UK;
        if (c == FRANCE) {
            System.out.println("Ok");
        }
    }
}

enum Country {FRANCE, UK};

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