How can I wrap a Java enum and still iterate over it?

How can I have an abstract enum, or some kind of base enum?

In my common code I'd like a notion of an enum placeholder, MyItems, without tying myself to a concrete enum. Then in each of my projects I would have a concrete implementation.

E.g. Common Code

public interface MyItems {
    // Marker interface
}

Project A

public enum Items implements MyItems {
     RED_CAR, BLUE_CAR, GREEN_CAR;
}

Project B

public e开发者_如何学Cnum Items implements MyItems {
    BROWN_TREE, GREEN_TREE;
}

This seems to work, but in my common code I can't write a loop over my interface enum, since it's not an enum. In my common code I'd like to write

for (MyItems item : MyItems.values())
    doSomething(item);

but I can't because my interface is just a marker interface, and it doesn't have a .values().

Any suggestions greatly appreciated. I don't know if I'm trying in completely the wrong way.

It doesn't really make sense to do this - because the values() method is static. To call it, you need to know the type you want to call it on.

The closest you could come would be to have:

public interface MyItemsFactory<T extends MyItems>
{
    Iterable<T> values();
}

and then implement that in some generic way, e.g.

public class EnumFactory<T extends Enum<T> & MyItems>
    implements MyItemsFactory<T>
{
    private final Class<T> clazz;

    public EnumFactory(Class<T> clazz)
    {
        this.clazz = clazz;
    }

    public Iterable<T> values()
    {
        return EnumSet.allOf(clazz);
    }
}

But the basic rule is that polymorphism and static methods don't mix. In your call:

for(MyItems item : MyItems.values())
    doSomething(item);

which implementation of MyItems would you expect it to iterate over? You could have loads of types implementing MyItems.

You could look into replacing the enums with the Type Safe Enum Pattern, which would allow you to implement an interface, with a values() method that returned all the values for a particular implementation.

Get the class and dig the values with Class.getEnumConstants() from it.