Java™ How To Program (Early Objects), Tenth Edition

Using an Interface

To use an interface, a concrete class must specify that it implements the interface and must declare each method in the interface with the signature specified in the interface declaration. To specify that a class implements an interface, add the implements keyword and the name of the interface to the end of your class declaration’s first line. A class that does not implement all the methods of the interface is an abstract class and must be declared abstract. Implementing an interface is like signing a contract with the compiler that states, “I will declare all the methods specified by the interface or I will declare my class abstract.”

Common Programming Error 10.6

Failing to implement any method of an interface in a concrete ...