Inner static enum as generic type?

Question

I am learning and experimenting with Java generics and come up with following piece of code which does not compile as expected. Result cannot be resolved. I stands for input, O for output.

public interface Stats<I, O> {
    O addItem (int index, I item);
}

public class AStats implements Stats<Item, Result> {
    public static enum Result {
        SUCCESS1,
        SUCCESS2,
        ERROR;
    }

    @Override
    public Result addItem (int index, Item item) {
        //valid code
    }
}

• Is there more elegant solution than declaring Result in a separate file?

• Is it bad in general to have a method which returns an instance of generic type?

Answer 1

1. Your classname is AStats.Result, not Result:

   public class AStats implements Stats<Item, AStats.Result> {
      ...
   }
   

2. I don't think that returning an instance of generic, inner type is a bad idea.