Object Oriented Design and Classes

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Object Oriented Design and Classes
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Exercises

• Design a phone book program. Your program should
  keep track of the name and phone number of your
  contacts. You should be able to add new contacts
  to your phone book and view your phone book.

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What is a class?

• Programming mechanism to support OOD
• Data and the methods that operate on that data
  collectively called members
• Example bank account class
• Provide structure for organizing programs

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Methods

• Methods operate on data
• accessors read data, provide access to data but
  do not change it
• mutators change data
• examples from bank account, zoo
• constructor builds a new object
• An object in an instance of a class
• class is a blueprint for objects

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BankAccount Class

• class BankAccount
• def __init__(self, initial_balance)
• self.balance initial_balance
• def deposit(self, amount)
• self.balance amount
• def withdraw(self, amount)
• self.balance - amount
• def checkBalance(self)
• print "Balance ", self.balance

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BankAccount Class

• def __init__(self, initial_balance)
• self.balance initial_balance
• __init__ method is the constructor
• Used to initialize members of the object
• First parameter is self the object on which the
  method/constructor is called
• Use dot notation (.) to reference members of the
  object

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BankAccount Class

• def deposit(self, amount)
• self.balance amount
• def withdraw(self, amount)
• self.balance - amount
• Deposit and withdraw are mutators
• they modify the data member balance
• First parameter is self
• Like functions, methods can take any number of
  parameters

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BankAccount Class

• def checkBalance(self)
• print "Balance ", self.balance
• checkBalance does not modify data members

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Creating and Using Objects

• b BankAccount(500)
• //Name Type(constructor parameters)

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Creating and Using Objects

• b BankAccount(500)
• //Name Type(constructor parameters)
• //how would you withdraw funds?
• b.withdraw(500)
• //object_name.method_name(params)

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Composing Objects

• An object can have a reference to another object
• class Name
• def __init__(self, first, last)
• self.first first
• self.last last
• def printName(self)
• print "Name ", self.first, " ",
  self.last
• class Employee
• def __init__(self, first, last, pay)
• self.name Name(first, last)
• self.pay pay
• def printEmployee(self)
• self.name.printName()
• print "\tPay rate ", self.pay

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Exercises

• Implement your phone book program.