Java枚举：列出类<？的枚举值扩展Enum>

Question

I've got the class object for an enum (I have a Class<? extends Enum> ) and I need to get a list of the enumerated values represented by this enum. The values static function has what I need, but I'm not sure how to get access to it from the class object.

Answer 1

Class.getEnumConstants

Answer 2

If you know the name of the value you need:

     Class<? extends Enum> klass = ... 
     Enum<?> x = Enum.valueOf(klass, "NAME");

If you don't, you can get an array of them by (as Tom got to first):

     klass.getEnumConstants();

Answer 3

using reflection is simple as calling Class#getEnumConstants() :

List<Enum<?>> enum2list(Class<? extends Enum<?>> cls) {
   return Arrays.asList(cls.getEnumConstants());
}

Answer 4

I am suprised to see that EnumSet#allOf() is not mentioned:

public static <E extends Enum<E>> EnumSet<E> allOf(Class<E> elementType)

Creates an enum set containing all of the elements in the specified element type.

Consider the following enum :

enum MyEnum {
  TEST1, TEST2
}

Simply call the method like this:

Set<MyEnum> allElementsInMyEnum = EnumSet.allOf(MyEnum.class);

Of course, this returns a Set , not a List , but it should be enough in many (most?) use cases.

Or, if you have an unknown enum :

Class<? extends Enum> enumClass = MyEnum.class;
Set<? extends Enum> allElementsInMyEnum = EnumSet.allOf(enumClass);

The advantage of this method, compared to Class#getEnumConstants() , is that it is typed so that it is not possible to pass anything other than an enum to it. For example, the below code is valid and returns null :

String.class.getEnumConstants();

While this won't compile:

EnumSet.allOf(String.class); // won't compile