1. Object-Orientated Programming

2. Object-Orientated Programming
Windows programs are event–driven:
nothing happens until the user moves the mouse, presses a key, selects from a menu, presses a command button, clicks on a tool bar

3. Object-Orientated Programming
Traditional programming methods and the languages that are used are not suitable for Windows environment
Instead Object-Orientated Programming (OOP) languages such as Visual basic, Visual C++ and Delphi have been developed to write Windows applications

4. Objects and Classes
The class is the blueprint that defines a related group of things
The class sets down the facts and rules the group has in common but does not store specific data
Once a class is defined in O.O.P. then instances of the class can be produced

5. Objects and Classes
Task 1: I want you to find all the other animal members of your group
Task 2: In your groups write down 5 common attributes associated with your groups “class” of animals
Task 3: In your groups write down 5 common activities carried out within your “class” of animals

6. Objects and Classes
The object is a member of the class. It takes the definition and adds data
Objects (routines) are collections of attributes and activities (called methods in Delphi and Visual Basic) that need to be performed such as…
Write code that executes as fast as possible
Occupies as little memory as possible

7. Objects in Windows
An object can be thought of as an independent procedure that contains both the instructions and data to perform some task and the code necessary to handle various messages it may receive
A dialog box in Windows is physically different from any other object
The code contains all the instructions necessary to draw the box on screen, display a text string in the title bar, and include a control-menu box in the top left-hand corner

8. Typical Facilities
The dialog box has attributes which are given values to define its colour and thickness of its border
The object also contains procedures which react to events which might occur, such as a user dragging the box or clicking the ‘Yes’ button
What happens when a procedure is carried out?
For example: other objects such as a message string and command buttons are displayed. They are separate objects with particular attributes and methods

9. Encapsulation
In third-generation languages such as Pascal, the programmer can choose to write structured, modular programs and divide the code up into a number of procedures
However, this is down to personal preference whether a task is broken up into one, two or three procedures
Nevertheless…

10. Encapsulation Within Object-Orientated programming…
Encapsulation is the concept of keeping all the relevant parts together such as procedures and data
An object usually represents some real concept such as dialog box, command button or list
Must take into consideration the procedures that will affect the object

11. Encapsulation
An object contains all that is required to make that particular aspect of the program carry out its tasks:
The procedures of methods that are required to respond to events that may occur
The data that is required by these procedures
Note the data is only accessed through the object.

12. O.O.P. Benefits
O.O.P. utilises member functions which means that only the object can access and control the data directly (Geography/History teacher scenario)
Variables are retained throughout the duration of the program
Whereas conventional programming uses routines which could accidentally access and alter the private data
Especially in the case of global variables which could be mucked-up via other procedures
With O.O.P. it’s difficult to alter/accidentally muck-up the already accomplished code
If the data needs to be altered in anyway, only the object that controls the data needs to be modified
Modifications can be carried out quickly and by one member of a programming team with the work being added to: inheriting base class characteristics

13. Inheritance Many objects are related to other objects in some way
Task 4: Chart
Many objects are related to other objects in some way
A sports car and a lorry are part of the Vehicle class
Humans, tigers and whales are members of the Mammal Class
You can define a new type of object
by amending the definition of a similar object
In object-orientated programming, this has the advantage of allowing the reuse of existing code, and is known as inheritance
Taking and adding to the features of an existing class
You cannot delete or change existing features and abilities

14. Mammal Class Human Class Tiger Class
Inheritance
Mammal Class
Correct
Human Class
Tiger Class
Properties: Methods:
Age Eat
Gender Breathe
Body Temp Sleep
Properties: Methods:
Age Eat
Gender Breathe
Body Temp Sleep
Addition. Properties: Methods:
Name Talk
Address
Properties: Methods:
Age Eat
Gender Breathe
Body Temp Sleep
Addition. Properties: Methods:
Species Hunt
Fur Colour

15. The man and the tiger will have to run the same way.
Inheritance
Mammal Class
If you are creating a computer game that requires a run method: it is best to put it into the man object or tiger object. Defining it within the mammal class is too restrictive.
Incorrect:
The Run method is too specific at this stage: humans run with two legs and tigers with four
Human Class
Tiger Class
The man and the tiger will have to run the same way.
Properties: Methods:
Age Eat
Gender Breathe
Body Temp Run
Properties: Methods:
Age Eat
Gender Breathe
Body Temp Run
Addition. Properties: Methods:
Name Talk
Address
Properties: Methods:
Age Eat
Gender Breathe
Body Temp Run
Addition. Properties: Methods:
Species Hunt
Fur Colour

16. Polymorphism
Two or more classes that are derived from the same base class are said to be polymorphic
Polymorphism means that two objects may share many characteristics but have unique features of their own
When new classes are derived from a base class they may redefine some of the base methods
Polymorphism allows for objects of different classes to recognise and process the same messages, using either the same or different methods

17. Polymorphism
Inherited Polymorphism is used when objects of different classes process the same message because they inherit it from a common ancestor
In the HUMAN and TIGER example, the method for sleep could be defined the same way
Independent Polymorphism is used when different classes use the same field or method name for different values or activities

18. Polymorphism Containment
We could define Run method for HUMANS which would outline the mechanics of running (good for a computer game), but this method would not work for the TIGER class, which uses four legs to run
Therefore, the Run method cannot be put into the MAMMAL class but a Run method could be put into each of the HUMAN and TIGER classes
Containment
Objects can contain other objects
You could create a Vehicle Class that contains objects such as ‘engine’ and ‘equipment’
A ‘House’ class could contain several ‘Room’ objects