7.6. Interfaces

Extending classes using single implementation inheritance creates new class types. A superclass reference can refer to objects of its own type and its subclasses strictly according to the inheritance hierarchy. Because this relationship is linear, it rules out multiple implementation inheritance, i.e., a subclass inheriting from more than one superclass. Instead Java provides interfaces, which not only allow new named reference types to be introduced, but also permit multiple interface inheritance.

Generic interfaces are discussed in Section 14.2, p. 666.