Get Values from Enum Known Only At Runtime

问题:

I need to get all the values from an enum, whose type will only be known at runtime. I've come up with the following, but would like to know if anyone knows a better way:

enum TestEnum  {
  FOO,
  BAR
}

Enum[] getValuesForEnum(Class type) {
  try {
    Method m = type.getMethod("values");
    return (Enum[])m.invoke(null);
  } catch (Exception e) {
    throw new RuntimeException(e);
  }
}

Class testEnum = Class.forName("TestEnum");
getValuesForEnum(testEnum);

Thanks!

回答1:

Use the available API instead:

T[] getValuesForEnum(Class<T> type) {
  return type.getEnumConstants();
}

From the Javadoc:

Returns the elements of this enum class or null if this Class object does not represent an enum type.

Note that I have turned your method into generic to make it typesafe. This way you need no downcasts to get the actual enum values from the returned array. (Of course, this makes the method so trivial that you can omit it and call type.getEnumConstants() directly :-)

回答2:

Here's a variant of Kevin Stembridge's answer that preserves the type (avoiding downcasts), whilst still guarding against being called with a non-enum type:

static <E extends Enum<E>> E[] getValuesForEnum(Class<E> clazz) {
    return clazz.getEnumConstants();
}

回答3:

I use type.getEnumConstants().

回答4:

I think this works:

Enum<?>[] getValuesForEnum(Class<Enum<?>> enumType) {
    return enumType.getEnumConstants();
}