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 .
Also, you may not use the private and protected specifiers when declaring members of an interface. However, this is unnecessary, because interfaces and their methods are implicitly abstract. You should not use abstract in your interface declarations or in your method declarations within interfaces.