The Interface Advantage

// Create Objects
ShopKeeper shopKeeper = new ShopKeeper("Larry");
Teacup teacup = new Teacup();
String treehouse = "Treehouse";

// Loop through Objects
Object[] objects = {shopKeeper, teacup, treehouse};

for (Object object : objects) {
    if (object instanceof Chattable) {
        String response = ((Chattable) object).chat();
        System.out.println(response);
    }
}

// Loop through Chattables
Chattable[] chattables = {shopKeeper, teacup};

for (Chattable chattable : chattables) {
    String response = chattable.chat();
    System.out.println(response);
}