The DrawableInComic interface defines one of the method requirements for the drawSpeechBalloon method with destination as an argument of the DrawableInComic type, which is the same type that the interface defines. The following is the first line in our sample code that called this method:

teddy.drawSpeechBalloon(winston, "How do you do?");

We called the method implemented in the SpiderDog class because teddy is an instance of SpiderDog. We passed a SpiderDog instance, winston, to the destination argument. The method works with the destination argument as an instance that implements the DrawableInComic interface. Hence, whenever we reference the destination variable, we will only be able to see what the DrawableInComic type defines.

We can easily understand what happens under the hood when Java downcasts a type from its original type to a target type, such as an interface to which the class conforms. In this case, SpiderDog is downcasted to DrawableInComic...