1. An Object-Oriented Approach to Programming Logic and Design
Chapter 2
Object-Oriented Programming Concepts

2. An Object-Oriented Approach to Programming Logic and Design
Objectives
Understand the basic principles of OOP
Define classes and create class diagrams
Understand public and private access
Instantiate and use objects
Understand inheritance
An Object-Oriented Approach to Programming Logic and Design

3. Objectives (continued)
Understand polymorphism
Understand protected access
Describe GUI classes as an example of built-in classes
Understand the advantages of OOP
An Object-Oriented Approach to Programming Logic and Design

4. An Overview of Object-Oriented Programming
Object oriented programming: focuses on the data and the methods to manipulate it
Attributes: characteristics that define an object
Class: a group or collection of objects with common properties
Instance: an existing object created from a class
An Object-Oriented Approach to Programming Logic and Design

5. An Overview of Object-Oriented Programming (continued)
Messages are passed to objects, requesting the objects to take actions
The same message works differently when applied to different objects
A module or procedure can process different types of data, without the need to write a separate version of the module or procedure
An Object-Oriented Approach to Programming Logic and Design

6. An Overview of Object-Oriented Programming (continued)
Objects can share or inherit traits of other objects that have already been created
Encapsulation and information handling are important features of OOP
Methods: procedures that process data
Polymorphism: the ability to create multiple methods with the same name that act differently when used with different objects
An Object-Oriented Approach to Programming Logic and Design

7. An Overview of Object-Oriented Programming (continued)
Inheritance: acquiring the traits of one’s predecessors
Encapsulation: combining an object’s attributes and methods into a single package
Information hiding: only an object’s own class should be able to alter that object’s attributes
Interface: the user interaction part of the object
An Object-Oriented Approach to Programming Logic and Design

8. Defining Classes and Creating Class Diagrams
Class: a category of things
Object: a specific instance of a class
Class definition: set of program statements that detail the objects attributes and methods
A class may contain three parts:
Class name: required
Data: optional
Methods: optional
An Object-Oriented Approach to Programming Logic and Design

9. Defining Classes and Creating Class Diagrams (continued)
Class diagram: rectangle with 3 sections
Class name
Attribute names and data types
Methods
An Object-Oriented Approach to Programming Logic and Design

10. Defining Classes and Creating Class Diagrams (continued)
An Object-Oriented Approach to Programming Logic and Design

11. Defining Classes and Creating Class Diagrams (continued)
An Object-Oriented Approach to Programming Logic and Design

12. Defining Classes and Creating Class Diagrams (continued)
An Object-Oriented Approach to Programming Logic and Design

13. Understanding Public and Private Access
Private access: data cannot be accessed by any method that is not part of the object’s class
Public access: other programs and methods may use the object’s methods
Access specifier: keyword that defines the access type
private
public
An Object-Oriented Approach to Programming Logic and Design

14. Understanding Public and Private Access (continued)
An Object-Oriented Approach to Programming Logic and Design

15. Understanding Public and Private Access (continued)
In class diagrams, access type is shown as a plus sign (+) for public, and a minus sign (–) for private
An Object-Oriented Approach to Programming Logic and Design

16. Understanding Public and Private Access (continued)
An Object-Oriented Approach to Programming Logic and Design

17. Instantiating and Using Objects
Instantiate – to create a class object, or instance of the class
Instantiation statement includes the class name and the object name
Ex. Employee myAssistant
An instantiated object has its own copy of the attributes and methods defined for the class
An Object-Oriented Approach to Programming Logic and Design

18. Instantiating and Using Objects (continued)
An Object-Oriented Approach to Programming Logic and Design

19. Instantiating and Using Objects (continued)
Method call: statement that invokes a procedure (causes the procedure to execute)
Advantage of OOP is that the programmer does not need all of the details in the method, just needs to use it (feature of encapsulation)
A program that uses a class object is a client of the class
An Object-Oriented Approach to Programming Logic and Design

20. Understanding Inheritance
Descendent (child) class: a new class that can inherit all of the attributes and methods of the original (parent) class, or can override the attributes and methods
Child class is more specific than the parent class
An Object-Oriented Approach to Programming Logic and Design

21. Understanding Inheritance (continued)
An Object-Oriented Approach to Programming Logic and Design

22. Understanding Inheritance (continued)
An Object-Oriented Approach to Programming Logic and Design

23. Understanding Inheritance (continued)
Inherited methods that are modified in the child class but have the same name are said to overload or override the parent class methods
Inheritance allows re-use of code
An Object-Oriented Approach to Programming Logic and Design

24. Understanding Inheritance (continued)
An Object-Oriented Approach to Programming Logic and Design

25. Understanding Inheritance (continued)
Child class will use its parent class methods unless the child class overrides or overloads the methods
Abstract class: a class intended to be a parent only and not to have objects instantiated from it
An Object-Oriented Approach to Programming Logic and Design

26. An Object-Oriented Approach to Programming Logic and Design
Using Polymorphism
Polymorphism: “many forms” of the same method
Same method call is carried out differently, depending on the context (usually, the type of data being used)
Each version of the method is written separately, but uses the same method name
An Object-Oriented Approach to Programming Logic and Design

27. Understanding Protected Access
Protected Access: only child classes can use a data field marked as protected
Protected access is denoted in class diagrams with the octothorpe (#) sign
An Object-Oriented Approach to Programming Logic and Design

28. Understanding Protected Access (continued)
An Object-Oriented Approach to Programming Logic and Design

29. Understanding Protected Access (continued)
An Object-Oriented Approach to Programming Logic and Design

30. Using a Predefined Class
Class Library: a collection of classes with related purposes
Example: classes for GUI components such as frames, buttons, labels, text boxes, etc.
Visual development environment used to create programs with a GUI user interface
An Object-Oriented Approach to Programming Logic and Design

31. Understanding the Advantages of OOP
Saves programming time:
Objects instantiated from previously created classes include appropriate, reliable methods and attributes
Inheritance allows the extension of existing classes to serve related, more specific purposes
Pre-existing objects can be used as ‘black-box” components without needing to know the full details
An Object-Oriented Approach to Programming Logic and Design

32. An Object-Oriented Approach to Programming Logic and Design
Summary
OOP focuses on the application’s data and the methods to manipulate the data
Object: consists of attributes and methods
Class: a collection of objects with common properties
Class definition and diagram has 3 parts: name, attributes, methods
Data hiding specifies that data can only be manipulated by the class that owns it
An Object-Oriented Approach to Programming Logic and Design

33. An Object-Oriented Approach to Programming Logic and Design
Summary (continued)
Types of data access: public, private, protected
Instantiation: creation of an object from a class
Parent class properties can be inherited or overwritten/overloaded by child classes
Class library: collection of related classes
OOP can create reusable components
An Object-Oriented Approach to Programming Logic and Design