Programming Clojure, 2nd Edition

Interfaces

In Java, the usual mechanism for supporting this form of abstraction is the interface. The interface mechanism provides a means for dispatching calls to an abstract function, specified in an interface definition, to a specific implementation based on the datatype of the first parameter passed in the call. In Java, the first parameter is implicit; it is the object that implements the interface.

The following are the strengths of interfaces:

• Datatypes can implement multiple interfaces.
• Interfaces provide only specification, not implementation, which allows implementation of multiple interfaces without the problems associated with multiple class inheritance.

The weakness of interfaces is that existing datatypes cannot be extended ...