Note that I often write an interface when I intend only one implementing class. Capture the concept first.
Again, note that I often write an abstract class that has protocol (abstract methods) for every method in any intended subclass. This lets me capture a common implementation, but keeps my concept clear as I subclass. I never need to ask instanceof and I never need to cast an object reference. Everything naturally fits together freeing my mind to think of other (higher level) things.
