OOP

1. OBJECT-ORIENTED
PROGRAMMING
Mimi OpkinsCECS 277

3. Objects Are Black Boxes
Code
Data
Message
Message

4. Objects are Building Blocks

6. Objects and Instances
 An object is a self-contained element of a
computer program that represents a related
group of features and is designed to
accomplish specific tasks
 Objects are also called instances.

7. Object-Oriented Terminology
Object Inheritance
Instance Class
Behavior Methods
State Variables
Encapsulation Message
Polymorphism Superclass

8. State and Behavior
 All real-world objects have state and behavior
 A software object maintains its state in
variables and its behavior in methods.

9. Instance Variables and Methods
 Variables and methods associated with a
particular object
 An instance variable is an item of information
that defines an attribute or state
 An instance method is used to implement
behavior

10. Object Diagram
Private
Implementation
Details
Public Interfaces
Public Interfaces
Public Interfaces Public Interfaces

11. Car Object Diagram
60 mph
Overdrive
Wipers Off
Change Gears
Turn on/off wipers
Accelerate Brake

12. Encapsulation
Hiding information in an object’s center and then
providing a public interface for interacting with
it is called encapsulation

13. Benefits of Objects
 Modularity – source code for an object can be
independent from the source code for other
objects
 Information Hiding – private information is kept
hidden from the public interface

14. Messages
Software objects
interact and
communicate by
sending messages
to each other
Rover, Speak!
Bark!
Bark!

15. Messages With More Meaning
Back Up
changeGears(reverse)

16. Message Components
 The object to whom the message is addressed
 The name of the method to perform
 Any parameters needed

17. Benefits of Messages
 Methods – an object’s behavior is expressed
through its methods so passing messages
supports all possible interaction between
objects
 Location – objects don’t need to be in the
same process or even on the same machine to
send and receive messages

18. Classes
 The most important feature of Object-Oriented
Programming
 Classes embody all features of a set of objects
 Define classes of objects
 Software blueprint

19. Definition of Class
 A class is a blueprint or prototype that defines
the variables and methods common to all
objects of certain kind.
 It is a template used to create multiple objects
with similar features

20. Class Variables and Methods
 A class variable is an item of information that
defines an attribute of an entire class.
 Class methods implement behavior for the
entire class.

21. Static Variables and Methods
 Static variables apply to the class itself and to all
of its instances
 Can access static variables and methods from
an instance of the class or directly by the class
 You don’t have to instantiate a class to use its
class variables and class methods
 Static methods only operate on class variables

22. Benefits of Classes
 Reusability – programmers can use the same
class and therefore the same code over and
over again to create different objects

23. Inheritance
 Inheritance is the mechanism that enables one
class to inherit all of the state and behavior of
another class
 Through inheritance, a class has all the
functionality of an existing class
 A new class can be created by only indicating
how it is different from an existing class

24. Superclass and Subclass
 A parent-child relationship
 A class that inherits from another class is a
subclass
 The class that gives the inheritance is the
superclass

25. Car Class Hierarchy
Car
SUV Mini Van Sports Car

26. Override
 Subclasses can override inherited methods and
provide specialized implementations for those
methods
 Overriding means to create a different method
definition for a method inherited from a subclass
 Overriding a method can be accomplished by
passing a different number of different types of
parameters

27. Benefits of Inheritance
 Specialized behavior – subclasses provide
specialized behaviors from the basis of
common variables and methods provided by
the superclass
 Abstract Classes – an abstract class defines
generic behavior
 Reuse – Don’t start code from scratch. Reuse
existing classes

28. Polymorphism
 By inheriting its superclass’ features, an
subclass is still a member of the superclass. It
can execute all of it’s methods as well as those
of the superclass. This ability to be both a
member of subclass and a superclass is called
polymorphism.
 In other words, a sports car is still a car

29. Comparison to Procedural
Languages
 Object-Oriented Programming
 Defines the “what” or the classes first
 Then the “how”

30. Procedure-Oriented
Programming
 First you identify the task to be performed
then:
1. Top-Down Approach -- by a step-wise
refinement, break the tasks into subtasks
2. Bottom-Up Approach – write procedures to
solve simple tasks and combine them into more
sophisticated procedures
 Most Programmers use a mixture of these
two approaches

31. Advantages of Object-Oriented
Programming
 Classes provide a convenient clustering
mechanism for methods
 The Object-Oriented structure is much
easier to grasp by the programmer or to
handle by teams of programmers
 Encapsulation – classes hide their data
representation from all code except their
own classes

32. Finding a Data-Related Bug
Global
Data
function
function
function
function
function
Object Data
Object Data
Object Data
method
method
method
method
method
Procedural Approach Object-Oriented Approach

33. Other Differences
 Modules
 Single Entity
 Forced Organization
 Classes
 Multiple Entities
 Natural Organization

34. Object-Oriented Design
Furry Household Pet Class
(Abstract)
Cat Class
Dog Class
Rabbit Class

35. An Object-Oriented Program
 When we write an Object-Oriented Program,
we design and construct a set of classes
 When the program runs, objects are created
from those classes
 We need to create the right set of classes to
accomplish what the program needs to do

36. Dragon State
 Color – yellow, red, green
 Attitude – mean, angry, playful
 Appetite – full, hungry

37. Dragon Behavior
 Get angry
 Calm down
 Eat a knight
 Breath fire

38. Reasons for Calling Methods
 To report a change to another object
 To tell the other object to change something
about itself
 To ask another object to do something

39. Dragon Scenario
 Dragon Object
 IamDead
Instance Method
 NumberofDragons
Class Variable
 ReduceDragons
Class Method
 Knight Object
 Sir Galahad
Instance Variable
 ChopOffDragonHead
Instance Method

40. Organizing Classes
 Determine if classes make up a class
hierarchy with subclasses
 Functionality that is common to multiple
classes can be put in superclasses
 Changes to a superclass are automatically
reflected in all their subclases

41. Monster Class Hierarchy
Monster
Flying Monster Swimming Monster

42. Flying Monster Class Hierarchy
Flying Monster
Mammal Reptile Amphibian
Four-Legged Flying Monster Two-Legged Flying Monster

43. Steps for Object-Oriented Programming
Design
1. Break down objects to their smallest
features
2. Look for commonality between the objects
3. Look for differences between the objects
4. Find the largest commonality between all
objects
5. Put the remaining common objects together
and repeat

44. Break Down Code to its Smallest
Features
Object Feature
Creatures Location, size, power level, capability to
attack, maneuverability
Power Pieces Must be drawn, location, power level
Bullets Capability to be fired
Main Character Capability to receive commands from the
user, capability to move around the maze
according to these commands, capability to
attack, location, size

45. Look For Commonality Between the
Objects
 Look for all the common relationships
between each of the objects
 The main difference between the creatures and
the main character is who controls them
 Have main character and creature share code
with the exception of the code to move them

46. Look For Difference Between the
Objects
 Find the differences between each of the
objects
 Look for relationships that unite and separate
all of the objects
 The bullets move and the power pieces don’t
 The computer controls creatures and the user
controls the main character

47. Find the Largest Commonality Between
All Objects
Draw Object
All Game Pieces

48. Put Remaining Common Objects
Together and Repeat
Draw Object
Creature Power Pieces/Bullets
Main Character

49. The “Big Example”
We’re going to take all the Object-Oriented
Programming and Object-Oriented Design
concepts and ideas and write a Science
Fiction Movie entitled…
“Programmers In Space”

50. Space Ship
Space Ship
Has a certain number of space shuttles
Has a certain number of imaging chambers
Has a certain number of officers
Has a certain number of aliens
Is located somewhere
Exists at a certain time
A typical Space Ship would have
Number of shuttles = 2
Location = sigma quadrant
Time period = 2253

51. Main Plot
Space Ship CECS is a new Space Ship
Number of imaging chambers = 1
Number of officers = 3
Captain = Danny
Senior Officer = Bob
Senior Officer = Jody
Number of aliens = 5

52. Humanoids
Humanoids
Have a certain number of legs
Have a certain number of arms
Have a certain number of eyes
Have a certain number of noses
Have a certain number of ears
Have a certain number mouths
Have a name
Have a certain sex
Have a favorite weapon
Have a beverage preference

53. Humanoids (continued)
A Standard Humanoid would start with
Number of legs = 2
Number of arms = 2
Number of eyes = 2
Number of noses =1
Number of ears =2
Number mouths = 1
When someone asks for your name
Tell them your name

54. Aliens
Aliens extend the idea of Humanoids
An Alien
Has non-standard ears
A certain “look”
A prophetic saying
Some level of meanness
A certain quantity of dimodium phosphate tubes
For a given Alien
It will look evil
It will start out the day calm
It will not yet have captured any dimodium phosphate tubes

55. Alien Instance Variables and
Methods
Drink Beverage
Level of meanness goes up by one
How Mean Am I
Tell them how mean I am

56. Alien Class Variables and
Methods
Prophetic Saying
Same saying for all aliens of a given species
Repeat Prophetic Saying
Retrieve it from the sacred book

57. Passing Parameters
Capture Dimodium Phosphate Tubes (# of tubes)
Increase the quantity of dimodium phosphate tubes by
the (# of tubes) amount
Gloat that you have captured (# of tubes) of dimodium
phosphate
Repeat Prophetic Saying
Retrieve it from the sacred book

58. Main Routine
There is a Space Ship called CECS
Number of imaging chambers = 1
Number of officers = 3
Captain = Danny
Senior Officer = Bob
Senior Officer = Jody
Number of aliens = 5
There is a new Human called Jennifer
Jennifer is female
Jennifer favor weapon is a keyboard
Jennifer prefers to drink coffee

59. Main Routine (continued)
There is a new Alien name Bernie
Bernie is male
Bernie has pointy ears
Bernie’s favorite weapon is a test tube
Bernie prefers to drink Pepsi
The prophetic saying spoken by Bernie’s race is “What’s
the status of that ticket?”
Bernie drinks some Pepsi
Bernie tells Jennifer how mean he is
Bernie captures 23 tubes of dimodium phosphate
Bernie quotes his prophetic saying

60. Resources for this Presentation
 Campione, Mary and Walrath, Kathy. The Java Tutorial Second
Edition: Object-Oriented Programming for the Internet. Addison-
Wesley. Reading, Massachusetts. 1998.
 Claerbout, Johannes. Don’t Fear the Oop!.
http://sepwww.standford.edu/sep/josman/oop/oop1.htm. 1998.
 Horstmann, Cay and Cornell, Gary. Core Java 2: Volume 1 –
Fundamentals. Sun Microsoft Press. Palo Alto, California. 1999.
 Lemay, Laura and Cadenhead, Rogers. Teach Yourself Java 2 in 21
Days. Sams Publishing. Indianapolis, Indiana. 1999.
 Weber, Joseph L. Special Edition: Using Java 2 Platform. Que
Publishers. 1999.