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Note that each method of the class ForwardingCalendar redirects to methods of the contained class instance (CalendarImplementation), and receives back return values. This is the forwarding mechanism. This class is largely independent of the implementation of the class CalendarImplementation. ThereforeConsequently, any future changes to the latter will not break CompositeCalendar which inherits from ForwardingCalendar. When CompositeCalendar's overriding after() method is invoked, it performs the necessary comparison by using the local version of the compareTo() method as required. Using super.after(when) forwards to the ForwardingCalendar which invokes the CalendarImplementation's after() method. In this case, CalendarImplementation's compareTo() method gets called instead of the overriding version in CompositeClass that was inappropriately called in the noncompliant code example, as a product of polymorphism.
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