november 28, 2005icp: chapter 9: object oriented programming 1 introduction to computer programming...

November 28, 2005 ICP: Chapter 9: Object Oriented Programming

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Introduction to Computer Programming

Chapter 9: Object Oriented Programming

Michael Scherger

Department of Computer Science

Kent State University

November 28, 2005 ICP: Chapter 9: Object Oriented Programming

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Contents

• Creating objects of different classes in the same program

• Allow objects to communicate with each other

• Combining classes

• Inheritance

• Overriding method definitions

November 28, 2005 ICP: Chapter 9: Object Oriented Programming

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Blackjack Game

• Example: Blackjack Game– Imports: Cards, Games

November 28, 2005 ICP: Chapter 9: Object Oriented Programming

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Sending and Receiving Messages

• Sending a Message– When one object tells

another object to perform some action or function

hero = Player()invader = Alien()

• • •

def hero.blast(self, enemy):

enemy.die()

November 28, 2005 ICP: Chapter 9: Object Oriented Programming

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Sending and Receiving Messages

• Receiving a Message– The action of executing the receiving the

message from the calling object and performing the appropriate method

November 28, 2005 ICP: Chapter 9: Object Oriented Programming

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Sending and Receiving Messages

• Example: Alien Blaster Program

November 28, 2005 ICP: Chapter 9: Object Oriented Programming

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Combining Objects

• Objects can be “combined” to form other objects or collections of objects– A Car Class consists of individual Tires,

Engine, Seats,…individual parts that make up the whole

– A Zoo Class has a collection of other animals: Lions, Tigers, Bears, etc

– A FreeCheckingAccount is a type of CheckingAccount is a type of Account

November 28, 2005 ICP: Chapter 9: Object Oriented Programming

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Combining Objects

• Creating the Card Class– A playing card has a “rank” and a “suit”

• Constants• Constructor initializes a single Card• __str__ is used to print out the rank and suit as a

two character string

November 28, 2005 ICP: Chapter 9: Object Oriented Programming

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Combining Objects

• Creating the Hand Class– The Hand class is a collection of Card objects

• Uses a list• __str__ prints out the contents of each hand• clear() clears the hand of cards• add() adds a card to the list• give() gives a card to another hand

November 28, 2005 ICP: Chapter 9: Object Oriented Programming

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Combining Objects

• Using Card Objects

• Combining Card Objects Using a Hand Object

• Example: Playing Cards Program

November 28, 2005 ICP: Chapter 9: Object Oriented Programming

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Using Inheritance to Create New Classes

• Create new classes from old– “is_a” relationship– Single inheritance– Multiple inheritance

November 28, 2005 ICP: Chapter 9: Object Oriented Programming

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Extending a Class Through Inheritance

• Creating a Base Class– Same base classes as before

• Inheriting from a Base Class– A “deck” is a special type of hand

• It has 52 cards (populate method)• You can deal from a deck• You can shuffle a deck

November 28, 2005 ICP: Chapter 9: Object Oriented Programming

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Extending a Class Through Inheritance

• Example: Playing Cards 2.0 Program

November 28, 2005 ICP: Chapter 9: Object Oriented Programming

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Altering the Behavior of Inherited Methods

• Creating a Base Class

November 28, 2005 ICP: Chapter 9: Object Oriented Programming

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Altering the Behavior of Inherited Methods

• Overriding Base Class Methods

November 28, 2005 ICP: Chapter 9: Object Oriented Programming

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Altering the Behavior of Inherited Methods

• Invoking Base Class Methods

November 28, 2005 ICP: Chapter 9: Object Oriented Programming

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Altering the Behavior of Inherited Methods

• Using the Derived Classes

November 28, 2005 ICP: Chapter 9: Object Oriented Programming

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Altering the Behavior of Inherited Methods

• Example: Playing Cards 3.0 Program

November 28, 2005 ICP: Chapter 9: Object Oriented Programming

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Understanding Polymorphism

November 28, 2005 ICP: Chapter 9: Object Oriented Programming

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Creating Modules

• Writing Modules

November 28, 2005 ICP: Chapter 9: Object Oriented Programming

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Creating Modules

• Importing Modules

November 28, 2005 ICP: Chapter 9: Object Oriented Programming

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Creating Modules

• Using Imported Functions and Classes

November 28, 2005 ICP: Chapter 9: Object Oriented Programming

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Creating Modules

• Example: Simple Game Program– Imports: Games

November 28, 2005 ICP: Chapter 9: Object Oriented Programming

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Blackjack Game (Again)

• Example: Blackjack Game– Imports: Cards, Games