Polymophism

Polymorphism happens and we can’t avoid it despite its silly sounding name.  We might have a baseclass which represents a basic document and we might subclass this generate ‘invoices’.  A different subclass might generate ‘cheques’. They may both have a method called print but the implementation of ‘print’ could be entirely different for the two base classes even though the same name ‘print’ is used in each case.  That’s polymorphism!