This class represents a user-written callback in an application that uses an instance of Cplex to solve a problem by means of the barrier optimizer. Cplex calls the user-written callback at the end of each barrier iteration. If an attempt is made to access information not available to an instance of this class, an exception is thrown.

The constructor and methods of this class are protected to make sure that they are used only to derive a user-written callback class or to implement the main method in it.