Object Oriented Design and Classes

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Object Oriented Design and Classes
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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