Java: How to get Values of an Enum Class from an Generic Type Object instance?

Question

I want to create an Enum editor, which takes an Enum type as its generic. E is a generic type, but restricted to be an Enum type. How can I get the values of the Enum class from the instance e?

public class ComboBoxEnumEditor<E extends Enum<E>>{
    public ComboBoxEnumEditor(E e) {
        // how to get values of E from e?
        // attemp1:
        List values = e.getClass().values();
        // attemp2:
        List values = ((Enum.class)e.getClass()).values();
        // attemp3:
        List values = ((Enum.class)e.getClass()).values();
        // none of the above works... 
    }
}

Say I have an Enum

public enum Location {
    Default( false, EAttributeLocation.MAIN_TABLE_IF_AVAILABLE ),
    Main( false, EAttributeLocation.MAIN_TABLE ),
    Overflow( false, EAttributeLocation.OVERFLOW_TABLE ),
    Separate( false, EAttributeLocation.SEPARATE_TABLE );
    ......
}

I want my ComboBoxEnumEditor be able to do

{
   ComboBoxEnumEditor(new Location());
}

Please help, thanks.

Community · Accepted Answer · 2017-05-23 12:25:57Z

14

It looks like you are looking for (but I may be mistaken)

Enum[] values = e.getClass().getEnumConstants();

or as mentioned by @pbabcdefp in this answer (big +1 for him) if you would like to have E[] instead of Enum[]

E[] values = e.getDeclaringClass().getEnumConstants();

Also based on

...which takes an Enum Class as its generic

your argument should probably be Class<E> clazz not E e itself so you could use it with ComboBoxEnumEditor(Location.class);. In that case you could simply use

E[] values = clazz.getEnumConstants();

edited May 23, 2017 at 12:25

CommunityBot

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answered Mar 6, 2015 at 21:20

Pshemo

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1 Comment

Mike Strobel Over a year ago

This is how I would do it. EnumSet.allOf(enumClass) can also be useful if you need to perform efficient set operations.

Paul Boddington · Accepted Answer · 2015-03-06 21:23:12Z

5

E[] arr = e.getDeclaringClass().getEnumConstants();

answered Mar 6, 2015 at 21:23

Paul Boddington

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5 Comments

Alex Over a year ago

Thanks a lot, this is exactly what I was looking for. I wish I could make both of you and Pshemo as answers. but he was a little bit faster.

Pshemo Over a year ago

e.getDeclaringClass() would be nice if OP really intend to use E e. But with argument Class<E> clazz instead E[] values = clazz.getEnumConstants(); compiles also fine.

Paul Boddington Over a year ago

@Alex No worries, Pshemo's answer is more detailed than mine. See this: stackoverflow.com/questions/27892675/…

Paul Boddington Over a year ago

@Pshemo I agree that using clazz is better. I should have mentioned it in my answer, so +1 to you. IMHO Java enums are excellent apart from the confusion caused by 3 ways to get constants (values(), getEnumConstants() and EnumSet.allOf()).

Pshemo Over a year ago

Yes that is true, we are screwed by fact that Enum doesn't have (maybe even abstract) values() method since it is dynamically added by compiler to each specific enum. It would make our life easier.

Necreaux · Accepted Answer · 2015-03-06 21:28:03Z

0

Short answer... You can't. Doing this is not valid syntax since you can't instantiate an enum:

ComboBoxEnumEditor(new Location());

Instead, you need to pass the class of your enum and change your method signature for that, e.g.

ComboBoxEnumEditor(Location.class);

edited Mar 6, 2015 at 21:28

answered Mar 6, 2015 at 21:21

Necreaux

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