Introduction to Objects

1. Introduction to Objects Adapted from “TEN STEPS TO OBJECT-SPEAK” a CPT Tech Talk by Joy Starks September 17, 1999

2. OBJECTIVES • Discuss the history of Object Oriented Technology (OT) • Describe basic concepts of OT • Define terms in Object Oriented Analysis & Design (OAD) and Programming (OOP) • Relate definitions to real-world examples • Mention some benefits of OT • Practice by Example

3. HISTORY OF OT • 1969 • Dr. Kristin Nygaard of Norway • Model fjord and movement of ships passing through it

4. HISTORY OF OT • The Problem • structured programming separates data from procedures • The Solution • Object Oriented Programming • model each component (data and procedure) as a single unit • model relationships between components

5. Objects and Classes Operations Requests Attributes Inheritance Encapsulation Polymorphism OT BASIC CONCEPTS

6. WHAT’S AN OBJECT? NOUN • Anything, real or abstract, about which we store data • Dr. Nygaard’s objects • mathematical models of boats • physical aspects of the fjord being analyzed • Other Examples • an invoice, an organization, a screen with which a user interacts, a drawing, an airplane, an order-filling process...

7. WHAT’S AN OPERATION? VERB • An activity that reads or manipulates data of an object • Dr. Nygaard’s operations • boats float, sink, move etc. • Other Examples • calculating a total, checking a balance, adding a new employee, changing an address, deleting a customer ...

8. HOW OBJECTS COMMUNICATE Adverb • An object is sent a message, which in turn causes an operation to be invoked • Sometimes the operation returns a response

9. Adjective WHAT’S AN ATTRIBUTE? • Characteristics that add detail to an object • Dr. Nygaard’s attributes • color, weight, size, etc. • Other Examples • someone’s name or address, an employee’s title, a book’s author , a part number, a room’s dimensions

10. INHERITING ATTRIBUTES • Objects can be decomposed into other objects • Generalization hierarchy • Supertype versus subtype • An object inherits the attributes in its parent class

11. SAMPLE GENERALIZATION HIERARCHY

12. WHAT ARE CLASSES? • An object type or object class is a category of an object that has similar characteristics and behavior • Example: employee or student • A class acts as a template or blueprint for object instances

13. OBJECT INSTANCES Proper Noun • An object instance is a specific example of an object type • Examples • John P. Smith, Invoice #12356 • And just to make it all really confusing, object instances are sometimes called objects!

14. ENCAPSULATION • The process of making implementation details of an object transparent to a user • Packaging data and operations together • Allows for information hiding • The black box approach

15. POLY-WHAT? • Polymorphism • the ability of two or objects to respond to the same message, each in its own way • an instruction is given using a generalized, rather than specific, detailed command • while specific actions would be different, results are the same • Example • Animal: Speak • Dogs bark; cats meow

16. SOME BENEFITS OF OBJECTS • Reusability • classes can be reused or inherited • Stability • over time, classes become more stable • Easier Design • black box concept • Faster Design • create applications from existing components

17. Practicing • A mammal is an object • Bear, buffalo, whale, and dolphin are subtypes • Yogi, Wilbur, and Smokey are instances of the Bear subtype • Eye color, ear size, and weight are attributes

18. VCR A Sony VCR My VCR, Serial #9234 Playback, record, and audio dubbing the VCR contains complex components that we assume work Use the remote control object subtype messages object instance operations object encapsulation Your Turn Match each VCR example on the left to the object-oriented term on the right.

19. Your Turn: Matching • VCR IS an object • A Sony VCR is an object subtype • Serial #9234 of Sony VCR is an object instance • Playback, record, and audio dubbing are examples of VCR operations • The concept that the VCR contains complex components you assume work is encapsulation • When you use a remote control, you are sending requests to the VCR

20. Objects are Models • A MODEL . . . • represents an aspect of reality • helps us to understand reality • assists us in inventing systems or redesigning business areas • should be simpler than reality • for example, model cars are simpler thana real car

21. OBJECT STRUCTURE DIAGRAM • Large rectangle with two horizontal dividing lines • Top third • object name • Middle third • object attributes • Bottom third • object methods

22. SAMPLE OBJECT STRUCTURE DIAGRAM TRAFFIC LIGHT Color Turn Red Turn Yellow Turn Green The operations are described in terms of what they do -- not how they do it.

23. VCR Buttons On-screen Messages Play Rewind Fast Forward Stop Record YOU TRY ONE ... • Draw an object structure diagram for the VCR object

24. Summary of Terminology • Objects, Classes, Operations, Attributes • Inheritance, Encapsulation, Polymorphism • Generalization Hierarchies • Object Structure Diagrams • Event Diagrams

25. The End