public class Test {

  public static void main(String[] args) {
    Buy buy1 = new Buy();
    buy1.buy(5, Thing.A, new Seller());

  }

}

class Seller {
}

interface Buyer<E extends Enum<E>> {

  void buy(int numOfItem, E e, Seller seller);
}

enum Thing {

  A, B, C;
}

class Buy implements Buyer<Thing> {

  public void buy(int numOfItem, Thing e, Seller seller) {
System.out.println("Buying "+numOfItem+ " " + e);
  }
}