Java SE. Урок 24. Интерфейсы

Interfaces are somewhat similar to regular classes and are most closely related to abstract classes, but have some differences and are not classes. All methods declared in an interface are automatically treated as public abstract, and all fields are treated as public static final, even if they are not declared as such. A class can implement any number of interfaces specified after the implements keyword. After this, the class must implement all methods derived from the interfaces or declare itself abstract. Multiple inheritance is allowed between interfaces, which is accomplished using the extends keyword. An unspoken rule is to append I to the interface name (Car - ICar).