Interface

An interface is a contract in the form of a collection of method and constant declarations. When a class implements an interface, it promises to implement all of the methods declared in that interface.

You use an interface to define a protocol of behavior that can be implemented by any class anywhere in the class hierarchy. Interfaces are useful for the following:

• Capturing similarities among unrelated classes without artificially forcing a class relationship.
• Declaring methods that one or more classes are expected to implement.
• Revealing an object's programming interface without revealing its class.