A remote control is an interface between you and your TV. An Interface in Java is not actually a class. Sun defines it as the place to "define a collection of method definitions and constant values. It can later be implemented by classes that refer to this interface with the 'implements' keyword". Remember that an Interface will define, but not implement methods. In essence, Interfaces are contracts for how objects will communicate with each other. When you try to understand a collection of classes in a package, look to the Interfaces first to understand the responsibilities of the package.