The class must either implement all the methods in the interface or be an abstract class. This example shows a class that implements only some of the methods declared in an interface. A subclass must implement the missing method. It is a compile error to declare a method as private or protected in an interface. Any method without an access level in an interface is a public method.
All fields are public static and final.
Declaring a field to be any other access level except public is a compile error. If no access level is given, it defaults to public. If a field is not explicitly declared to be static or final, the field is still static and final. You may be tempted to use interfaces as a place to put program contants. Usually a constant belongs to some abstraction.