如何找出EnumMap中使用的枚举？ [英] How do I find out the enum used in an EnumMap?

问题描述

我有一个带有内部枚举和EnumMap的测试类，如下所示。如何找出EnumMap中使用的枚举？

I have a test class with an internal enum and an EnumMap like the following. How do I find out which enum is used within the EnumMap?

enum MyEnum { ENUM1, ENUM2 }
EnumMap<MyEnum, String> emap = new EnumMap<>( MyEnum.class );
public void discover() {
  Class<?> eclass = ???;
  System.out.println( eclass );
}

应打印

MyEnum.class

MyEnum.class

推荐答案

如果映射不为空，您可以检索一个键并检查其类别。否则，唯一的方法是通过反射访问EnumMap的 keyType 私有字段（该字段不会通过公共API公开）。

If the map is not empty, you can retrieve one key and check its class. Otherwise the only way is to access the keyType private field of the EnumMap via reflection (the field is not exposed through the public API).

在第一种情况下，您可以这样做：

In the first case you can do:

Iterator<?> it = map.keySet().iterator();
while (it.hasNext()) {
  Object key = it.next();
  if (key != null) return key.getDeclaringClass();
}

在第二种情况下（显然也适用于非空枚举），您可以用途：

In the second case (which obviously also works for non empty enums) you can use:

private static Class<?> enumMapType(EnumMap<?, ?> map) {
  try {
    Field keyType = EnumMap.class.getDeclaredField("keyType");
    keyType.setAccessible(true);
    return (Class<?>) keyType.get(map);
  } catch (IllegalAccessException | NoSuchFieldException e) {
    throw new AssertionError("Could not find EnumMap type", e);
  }
}

如果内部执行 EnumMap 进行更改，最好能找到解决您需求的方法。

This could break if the internal implementation of EnumMap changes and it would be better to find a way around your requirement.

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