Polymorphically convert Java enum values into a list of strings

Question

I have a handful of helper methods that convert enum values into a list of strings suitable for display by an HTML <select> element. I was wondering if it's possible to refactor these into a single polymorphic method.

This is an example of one of my existing methods:

/**
 * Gets the list of available colours.
 * 
 * @return the list of available colours
 */
public static List<String> getColours() {
  List<String> colours = new ArrayList<String>();

  for (Colour colour : Colour.values()) {
    colours.add(colour.getDisplayValue());  
  }

  return colours;
}

I'm still pretty new to Java generics, so I'm not sure how to pass a generic enum to the method and have that used within the for loop as well.

Note that I know that the enums in question will all have that getDisplayValue method, but unfortunately they don't share a common type that defines it (and I can't introduce one), so I guess that will have to be accessed reflectively...?

Thanks in advance for any help.

Answer 1

using Class#getEnumConstants() is simple:

static <T extends Enum<T>> List<String> toStringList(Class<T> clz) {
     try {
        List<String> res = new LinkedList<String>();
        Method getDisplayValue = clz.getMethod("getDisplayValue");

        for (Object e : clz.getEnumConstants()) {
            res.add((String) getDisplayValue.invoke(e));

        }

        return res;
    } catch (Exception ex) {
        throw new RuntimeException(ex);
    }
}

this is not completely typesafe since you can have an Enum without a getDisplayValue method.