Apple Certification Exam 9L0-509

Note that this is a bit of a contrived example and that the drawable objects are not fully defined 9L0-509 (no constructors or data) but it should give you the general idea of the power of defining an interface. Once the objects are constructed, the code that calls the interface does not know any of the implementation details of the called objects, only that of the interface. 9L0-402 dumps The object GraphicalDrawingBoard is a placeholder meant to represent the thing onto which the object will be drawn, i.e. the video memory, drawing buffer, printer.

Note that there is a great temptation to add concrete member functions and data to pure abstract base classes. This must be resisted and in general it is a sign that the interface is not well factored. Data and concrete member functions tend to imply a particular 9L0-509 implementation and as such can inherit from the interface but should not be that interface. Instead if there is some commonality between concrete classes, creation of abstract class which inherits its interface from the pure abstract class and defines the common data and member functions of the concrete classes works well. Some care should be taken to decide whether inheritance or aggregation should be used. Too many layers of inheritance can make the maintenance and usage of a class difficult. Generally, the Testking 9L0-402 maximum accepted layers of inheritance is about 3, above that and refactoring of the classes is generally called for. A general test is the "is a" vs "has a", as in a Square is a Rectangle, but a Square has a set of sides.