方便地在enum和int / String之间映射 [英] Conveniently map between enum and int / String

问题描述

当使用只能获取有限数量的值的变量/参数时，我尝试始终使用Java的 enum ，如

When working with variables/parameters that can only take a finite number of values, I try to always use Java's enum, as in

public enum BonusType {
  MONTHLY, YEARLY, ONE_OFF
}

只要我留在我的代码中，那就行了。但是，我经常需要与其他使用纯文本 int （或 String ）的代码接口，或者我需要从数据库读取/写入数据，数据存储为数字或字符串。

As long as I stay inside my code, that works fine. However, I often need to interface with other code that uses plain int (or String) values for the same purpose, or I need to read/write from/to a database where the data is stored as a number or string.

在这种情况下，我想要一个方便的方法来将每个枚举值与一个整数相关联，这样我可以转换这两种方式（换句话说，我需要一个可逆枚举）。

In that case, I'd like to have a convenient way to associate each enum value with a an integer, such that I can convert both ways (in other words, I need a "reversible enum").

to int is easy：

Going from enum to int is easy:

public enum BonusType {
  public final int id;

  BonusType(int id) {
    this.id = id;
  }
  MONTHLY(1), YEARLY(2), ONE_OFF(3);
}

然后我可以访问int值 BonusType x = MONTHLY;然而，我可以看到没有一个好的方法，反向，即从int到枚举。。int id = x.id; 。

Then I can access the int value as BonusType x = MONTHLY; int id = x.id;.

理想情况下，像

BonusType bt = BonusType.getById(2); 

我可以想出的唯一解决方案是：

The only solutions I could come up with are:

• 在枚举中加入一个查找方法，使用 BonusType.values（）填充一个地图int - > enum然后缓存并使用它进行查找。会工作，但是我必须将这个方法同样复制到我使用的每个枚举： - （。


• 将lookup方法放入一个静态实用程序类中，然后我只需要一个lookup方法，但是我不得不使用反射来让它为任意枚举工作。

• Put a lookup method into the enum, which uses BonusType.values() to fill a map "int -> enum", then caches that and uses it for lookups. Would work, but I'd have to copy this method identically into each enum I use :-(.
• Put the lookup method into a static utility class. Then I'd only need one "lookup" method, but I'd have to fiddle with reflection to get it to work for an arbitrary enum.

任何其他想法/见解？

推荐答案

http://www.javaspecialists.co.za/archive/Issue113.html

解决方案开始时类似于你的int值作为枚举定义的一部分，然后继续创建一个基于泛型的查找实用程序：

The solution starts out similar to yours with an int value as part of the enum definition. He then goes on to create a generics-based lookup utility:

public class ReverseEnumMap<V extends Enum<V> & EnumConverter> {
    private Map<Byte, V> map = new HashMap<Byte, V>();
    public ReverseEnumMap(Class<V> valueType) {
        for (V v : valueType.getEnumConstants()) {
            map.put(v.convert(), v);
        }
    }

    public V get(byte num) {
        return map.get(num);
    }
}

这个解决方案很好， with reflection'，因为它是基于所有枚举类型隐式继承Enum接口的事实。

This solution is nice and doesn't require 'fiddling with reflection' because it's based on the fact that all enum types implicitly inherit the Enum interface.

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