However, whereas a class can extend only one other class, an interface can extend any number of interfaces. The list of superinterfaces is a comma-separated list of all the interfaces extended by the new interface. The interface body contains method declarations for all the methods included in the interface. All methods declared in an interface are implicitly public and abstract. An interface can contain constant declarations in addition to method declarations.
All constant values defined in an interface are implicitly public, static, and final.
An interface defines a protocol of behavior. A class that implements an interface adheres to the protocol defined by that interface. To declare a class that implements an interface, include an implements clause in the class declaration. Your class can implement more than one interface, so the implements keyword is followed by a comma-separated list of the interfaces implemented by the class. When you define a new interface, you are defining a new reference data type.