Pure virtual classes

• Get objects to interact with each other: need conformance to a set of mutually agreed methods
• In other words, need an interface
• All classes derived from the interface implement the interface methods as declared in the interface
• Can guarantee the formal behaviour of all derived objects
• In C++, an interface is known as a pure virtual class: a class consisting only of method declarations and no data fields
• A pure virtual class has no constructor -- no object of that class can ever be created (only objects of derived classes)
• A pure virtual class may have a virtual destructor to permit correct destruction of derived objects
• All methods (except the destructor) are declared as follows: returnType methodName(args) = 0;
• All derived classes must implement all methods